Davis 1899

Davis 1899

(Parte 1 de 4)

The Geographical Cycle Author(s): William M. Davis Source: The Geographical Journal, Vol. 14, No. 5 (Nov., 1899), p. 481-504 Published by: Blackwell Publishing on behalf of The Royal Geographical Society (with the Institute of British Geographers) Stable URL: http://www.jstor.org/stable/1774538 Accessed: 12/09/2008 14:49

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http://www.jstor.org continental coast, whichever it proves to be, along the Pacific to the meridian of Peter island.

Magnetic observations, deep-sea soundings, and dredgings would be taken throughout the three seasons; but, looking to the un- certain movements of the pack-ice, and to our ignorance of the conditions obtaining over the unknown area, a very wide discretion will be given to the leader of the expedition.

Simultaneously, the German expedition would proceed to its station at Kerguelen island, and thence to the scene of its labours, and, we hope, its discoveries. The ENDERBY or YALDIVIA and WEDDELL quadrants certainly comprise investigations of equal im- portance, including the discovery of that part of the continental land south of the Weddell sea, which is believed to comprise rocks other than volcanic. Here a landing-party will have work of even greater interest than that which lands in McMurdo bay. But it is not for me even to outline the contemplated German exploration, which has, doubtless, already been systematically planned by the able advisers of the expedition.

I believe that this great geographical enterprise is one of the most important that has ever been conceived. It will add largely to the sum of human knowledge, and, in many ways, will be of direct benefit to mankind. It is a beneficent work, a work which makes for peace and good fellowship among nations. It must rejoice the hearts of all geographers that the countrymen of HuImboldt, of Ritter, of Kiepert, of Richthofen, and of Neumayer should combine with the countrymen of Banks, of Rennell, of

Murchison, and of Sabine to achieve a grand scientific work which will redound to the honour of both nations.

By WILLIAM M. DAVIS, Professor of Physical Geography in Harvar University.

THE GENETIC CLASSIFICATION OF LAND-FORMS.-All the varied forms of the lands are dependent upon-or, as the mathematician would say, are functions of-three variable quantities, which may be called structure, process, and time. In the beginning, when the forces of deformation and uplift determine the structure and attitude of a region, the form of its surface is in sympathy with its internal arrangement, and its height depends on the amount of uplift that it has suffered. If its rocks were unchangeable under the attack of external processes, its surface would remain unaltered until the forces of deformation and uplift acted again; continental coast, whichever it proves to be, along the Pacific to the meridian of Peter island.

Magnetic observations, deep-sea soundings, and dredgings would be taken throughout the three seasons; but, looking to the un- certain movements of the pack-ice, and to our ignorance of the conditions obtaining over the unknown area, a very wide discretion will be given to the leader of the expedition.

Simultaneously, the German expedition would proceed to its station at Kerguelen island, and thence to the scene of its labours, and, we hope, its discoveries. The ENDERBY or YALDIVIA and WEDDELL quadrants certainly comprise investigations of equal im- portance, including the discovery of that part of the continental land south of the Weddell sea, which is believed to comprise rocks other than volcanic. Here a landing-party will have work of even greater interest than that which lands in McMurdo bay. But it is not for me even to outline the contemplated German exploration, which has, doubtless, already been systematically planned by the able advisers of the expedition.

I believe that this great geographical enterprise is one of the most important that has ever been conceived. It will add largely to the sum of human knowledge, and, in many ways, will be of direct benefit to mankind. It is a beneficent work, a work which makes for peace and good fellowship among nations. It must rejoice the hearts of all geographers that the countrymen of HuImboldt, of Ritter, of Kiepert, of Richthofen, and of Neumayer should combine with the countrymen of Banks, of Rennell, of

Murchison, and of Sabine to achieve a grand scientific work which will redound to the honour of both nations.

By WILLIAM M. DAVIS, Professor of Physical Geography in Harvar University.

THE GENETIC CLASSIFICATION OF LAND-FORMS.-All the varied forms of the lands are dependent upon-or, as the mathematician would say, are functions of-three variable quantities, which may be called structure, process, and time. In the beginning, when the forces of deformation and uplift determine the structure and attitude of a region, the form of its surface is in sympathy with its internal arrangement, and its height depends on the amount of uplift that it has suffered. If its rocks were unchangeable under the attack of external processes, its surface would remain unaltered until the forces of deformation and uplift acted again; continental coast, whichever it proves to be, along the Pacific to the meridian of Peter island.

Magnetic observations, deep-sea soundings, and dredgings would be taken throughout the three seasons; but, looking to the un- certain movements of the pack-ice, and to our ignorance of the conditions obtaining over the unknown area, a very wide discretion will be given to the leader of the expedition.

Simultaneously, the German expedition would proceed to its station at Kerguelen island, and thence to the scene of its labours, and, we hope, its discoveries. The ENDERBY or YALDIVIA and WEDDELL quadrants certainly comprise investigations of equal im- portance, including the discovery of that part of the continental land south of the Weddell sea, which is believed to comprise rocks other than volcanic. Here a landing-party will have work of even greater interest than that which lands in McMurdo bay. But it is not for me even to outline the contemplated German exploration, which has, doubtless, already been systematically planned by the able advisers of the expedition.

I believe that this great geographical enterprise is one of the most important that has ever been conceived. It will add largely to the sum of human knowledge, and, in many ways, will be of direct benefit to mankind. It is a beneficent work, a work which makes for peace and good fellowship among nations. It must rejoice the hearts of all geographers that the countrymen of HuImboldt, of Ritter, of Kiepert, of Richthofen, and of Neumayer should combine with the countrymen of Banks, of Rennell, of

Murchison, and of Sabine to achieve a grand scientific work which will redound to the honour of both nations.

By WILLIAM M. DAVIS, Professor of Physical Geography in Harvar University.

THE GENETIC CLASSIFICATION OF LAND-FORMS.-All the varied forms of the lands are dependent upon-or, as the mathematician would say, are functions of-three variable quantities, which may be called structure, process, and time. In the beginning, when the forces of deformation and uplift determine the structure and attitude of a region, the form of its surface is in sympathy with its internal arrangement, and its height depends on the amount of uplift that it has suffered. If its rocks were unchangeable under the attack of external processes, its surface would remain unaltered until the forces of deformation and uplift acted again; continental coast, whichever it proves to be, along the Pacific to the meridian of Peter island.

Magnetic observations, deep-sea soundings, and dredgings would be taken throughout the three seasons; but, looking to the un- certain movements of the pack-ice, and to our ignorance of the conditions obtaining over the unknown area, a very wide discretion will be given to the leader of the expedition.

Simultaneously, the German expedition would proceed to its station at Kerguelen island, and thence to the scene of its labours, and, we hope, its discoveries. The ENDERBY or YALDIVIA and WEDDELL quadrants certainly comprise investigations of equal im- portance, including the discovery of that part of the continental land south of the Weddell sea, which is believed to comprise rocks other than volcanic. Here a landing-party will have work of even greater interest than that which lands in McMurdo bay. But it is not for me even to outline the contemplated German exploration, which has, doubtless, already been systematically planned by the able advisers of the expedition.

I believe that this great geographical enterprise is one of the most important that has ever been conceived. It will add largely to the sum of human knowledge, and, in many ways, will be of direct benefit to mankind. It is a beneficent work, a work which makes for peace and good fellowship among nations. It must rejoice the hearts of all geographers that the countrymen of HuImboldt, of Ritter, of Kiepert, of Richthofen, and of Neumayer should combine with the countrymen of Banks, of Rennell, of

Murchison, and of Sabine to achieve a grand scientific work which will redound to the honour of both nations.

By WILLIAM M. DAVIS, Professor of Physical Geography in Harvar University.

THE GENETIC CLASSIFICATION OF LAND-FORMS.-All the varied forms of the lands are dependent upon-or, as the mathematician would say, are functions of-three variable quantities, which may be called structure, process, and time. In the beginning, when the forces of deformation and uplift determine the structure and attitude of a region, the form of its surface is in sympathy with its internal arrangement, and its height depends on the amount of uplift that it has suffered. If its rocks were unchangeable under the attack of external processes, its surface would remain unaltered until the forces of deformation and uplift acted again; and in this case structure would be alone in control of form. But no rocks are unchangeable; even the most resistant yield under the attack of the atmosphere, and their waste creeps and washes downhill as long as any hills remain; hence all forms, however high and however resistant, must be laid low, and thus destructive process gains rank equal to that of structure in determining the shape of a land-mass. Process cannot, however, complete its work instantly, and the amount of change from initial form is therefore a function of time. Time thus completes the trio of geographical controls, and is, of the three, the one of most frequent application and of most practical value in geographical description.

Structure is the foundation of all geographical classifications in which the trio of controls is recognized. The Alleghany plateau is a unit, a "region," because all through its great extent it is composed of widespread horizontal rock-layers. The Swiss Jura and the Pennsyl- vanian Appalachians are units, for they consist of corrugated strata. The Laurentian highlands of Canada are essentially a unit, for they consist of greatly disturbed crystalline rocks. These geographical units have, however, no such simplicity as mathematical units; each one has a certain variety. The strata of plateaus are not strictly horizontal, for they slant or roll gently, now this way, now that. The corrugations of the Jura or of the Appalachians are not all alike; they might, indeed, be more truly described as all different, yet they preserve their essential features with much constancy. The disordered rocks of the Laurentian highlands have so excessively complicated a structure as at present to defy description, unless item by item; yet, in spite of the free variations from a single structural pattern, it is legitimate and useful to look in a broad way at such a region, and to regard it as a structural unit. The forces by which structures and attitudes have been determined do not come within the scope of geo- graphical inquiry, but the structures acquired by the action of these forces serve as the essential basis for the genetic classification of geo-- graphical forms. For the purpose of this article, it will suffice to recognize two great structural groups: first, the group of horizontal structures, including plains, plateaus, and their derivatives, for which no single name has been suggested; second, the group of disordered structures, including mountains and their derivatives, likewise without a single name. The second group may be more elaborately subdivided than the first.

The destructive processes are of great variety-the chemical action, of air and water, and the mechaiical action of wind, heat, and cold, of rain and snow, rivers and glaciers, waves and currents. But as most of the land surface of the Earth is acted on chiefly by weather changes.

and running water, these will be treated as forming a normal group of destructive processes; while the wind of arid deserts and the ice of' and in this case structure would be alone in control of form. But no rocks are unchangeable; even the most resistant yield under the attack of the atmosphere, and their waste creeps and washes downhill as long as any hills remain; hence all forms, however high and however resistant, must be laid low, and thus destructive process gains rank equal to that of structure in determining the shape of a land-mass. Process cannot, however, complete its work instantly, and the amount of change from initial form is therefore a function of time. Time thus completes the trio of geographical controls, and is, of the three, the one of most frequent application and of most practical value in geographical description.

Structure is the foundation of all geographical classifications in which the trio of controls is recognized. The Alleghany plateau is a unit, a "region," because all through its great extent it is composed of widespread horizontal rock-layers. The Swiss Jura and the Pennsyl- vanian Appalachians are units, for they consist of corrugated strata. The Laurentian highlands of Canada are essentially a unit, for they consist of greatly disturbed crystalline rocks. These geographical units have, however, no such simplicity as mathematical units; each one has a certain variety. The strata of plateaus are not strictly horizontal, for they slant or roll gently, now this way, now that. The corrugations of the Jura or of the Appalachians are not all alike; they might, indeed, be more truly described as all different, yet they preserve their essential features with much constancy. The disordered rocks of the Laurentian highlands have so excessively complicated a structure as at present to defy description, unless item by item; yet, in spite of the free variations from a single structural pattern, it is legitimate and useful to look in a broad way at such a region, and to regard it as a structural unit. The forces by which structures and attitudes have been determined do not come within the scope of geo- graphical inquiry, but the structures acquired by the action of these forces serve as the essential basis for the genetic classification of geo-- graphical forms. For the purpose of this article, it will suffice to recognize two great structural groups: first, the group of horizontal structures, including plains, plateaus, and their derivatives, for which no single name has been suggested; second, the group of disordered structures, including mountains and their derivatives, likewise without a single name. The second group may be more elaborately subdivided than the first.

The destructive processes are of great variety-the chemical action, of air and water, and the mechaiical action of wind, heat, and cold, of rain and snow, rivers and glaciers, waves and currents. But as most of the land surface of the Earth is acted on chiefly by weather changes.

and running water, these will be treated as forming a normal group of destructive processes; while the wind of arid deserts and the ice of' frigid deserts will be considered as climatic modifications of the norm, and set apart for particular discussion; and a special chapter will be needed to explain the action of waves and currents on the shore-lines at the edge of the lands. The various processes by which destructive work is done are in their turn geographical features, and many of them are well recognized as such, as rivers, falls, and glaciers; but they are too commonly considered by geographers apart from the work that they do, this phase of their study being, for some unsatisfactory reason, given over to physical geology. There should be no such separation of agency and work in physical geography, although it is profitable to give separate consideration to the active agent and to the inert mass on which it works.

TIME AS AN ELEMENT IN GEOGRAPHICAL TERMINOLOGY.-The amount of change caused by destructive processes increases with the passage of time, but neither the amount nor the rate of change is a simple function of time. The amount of change is limited, in the first place, by the altitude of a region above the sea; for, however long the time, the normal destructive forces cannot wear a land surface below this ul- timate baselevel of their action; and glacial and marine forces cannot wear down a land-mass indefinitely beneath sea-level. The rate of change under normal processes, which alone will be considered for the present, is at the very first relatively moderate; it then advances rather rapidly to a maximum, and next slowly decreases to an indefinitely postponed minimum.

Evidently a longer period must be required for the complete denu- dation of a resistant than of a weak land-mass, but no measure in terms of years or centuries can now be given to the period needed for the effective wearing down of highlands to featureless lowlands. All historic time is hardly more than a negligible fraction of so vast a duration. The best that can be done at present is to give a convenient name to this unmeasured part of eternity, and for this purpose nothing seems more appropriate than a " geographical cycle." When it is possible to establish a ratio between geographical and geological units, there will probably be found an approach to equality between the duration of an average cycle and that of Cretaceous or Tertiary time, as has been indicated by the studies of several geomorphologists.

"THEORETICAL" GEOGRAPHY.-It is evident that a scheme of geo- graphical classification that is founded on structure, process, and time, must be deductive in a high degree. This is intentionally and avowedly the case in the present instance. As a consequence, the scheme gains a very " theoretical" flavour that is not relished by some geographers, whose work implies that geography, unlike all other sciences, should be developed by the use of only certain ones of the mental faculties, chiefly observation, description, and generalization. But nothing seems to me clearer than that geography has already suffered too long from frigid deserts will be considered as climatic modifications of the norm, and set apart for particular discussion; and a special chapter will be needed to explain the action of waves and currents on the shore-lines at the edge of the lands. The various processes by which destructive work is done are in their turn geographical features, and many of them are well recognized as such, as rivers, falls, and glaciers; but they are too commonly considered by geographers apart from the work that they do, this phase of their study being, for some unsatisfactory reason, given over to physical geology. There should be no such separation of agency and work in physical geography, although it is profitable to give separate consideration to the active agent and to the inert mass on which it works.

TIME AS AN ELEMENT IN GEOGRAPHICAL TERMINOLOGY.-The amount of change caused by destructive processes increases with the passage of time, but neither the amount nor the rate of change is a simple function of time. The amount of change is limited, in the first place, by the altitude of a region above the sea; for, however long the time, the normal destructive forces cannot wear a land surface below this ul- timate baselevel of their action; and glacial and marine forces cannot wear down a land-mass indefinitely beneath sea-level. The rate of change under normal processes, which alone will be considered for the present, is at the very first relatively moderate; it then advances rather rapidly to a maximum, and next slowly decreases to an indefinitely postponed minimum.

Evidently a longer period must be required for the complete denu- dation of a resistant than of a weak land-mass, but no measure in terms of years or centuries can now be given to the period needed for the effective wearing down of highlands to featureless lowlands. All historic time is hardly more than a negligible fraction of so vast a duration. The best that can be done at present is to give a convenient name to this unmeasured part of eternity, and for this purpose nothing seems more appropriate than a " geographical cycle." When it is possible to establish a ratio between geographical and geological units, there will probably be found an approach to equality between the duration of an average cycle and that of Cretaceous or Tertiary time, as has been indicated by the studies of several geomorphologists.

"THEORETICAL" GEOGRAPHY.-It is evident that a scheme of geo- graphical classification that is founded on structure, process, and time, must be deductive in a high degree. This is intentionally and avowedly the case in the present instance. As a consequence, the scheme gains a very " theoretical" flavour that is not relished by some geographers, whose work implies that geography, unlike all other sciences, should be developed by the use of only certain ones of the mental faculties, chiefly observation, description, and generalization. But nothing seems to me clearer than that geography has already suffered too long from the disuse of imlagination, invention, deduction, and the various other mental faculties that contribute towards the attainment of a well-tested explanation. It is like walking on one foot, or looking with one eye, to exclude from geography the " theoretical" half of the brain-power, which other sciences call upon as well as the "practical" half. Indeed, it is only as a result of misunderstanding that an antipathy is implied between theory and practice, for in geography, as in all sound scientific work, the two advance most amiably and effectively together. Surely the fullest development of geography will not be reached until all the mental faculties that are in any way pertinent to its cultivation are well trained and exercised in geographical investigation.

All this may be stated in another way. One of the most effective aids to the appreciation of a subject is a correct explanation of the facts that it presents. Understanding thus comes to aid the memory. But a genetic classification of geographical forms is, in effect, an explanation of them; hence such a classification must be helpful to the travelling,

.studying, or teaching geographer, provided only that it is a true and natural classification. True and natural a genetic classification may

,certainly be, for the time is past when even geographers can look on the forms of lands as "ready made." Indeed, geographical definitions and descriptions are untrue and unnatural just so far as they give the impression that the forms of the lands are of unknown origin, not sus- ceptible of rational explanation. From the very beginning of geography in the lower schools, the pupils should be possessed with the belief that geographical forms have meaning, and that the meaning or origin of so many forms is already so well assured that there is every reason to think that the meaning of all the others will be discovered in due time. The explorer of the Earth should be as fully convinced of this principle, and as well prepared to apply it, as the explorer of the sky is to carry physical principles to the furthest reach of his telescope, his spectro- scope, and his camera. The preparation of route-maps and the deter- mination of latitude, longitude, and altitude for the more important points is only the beginning of exploration, which has no end till all the facts of observation are carried forward to explanation.

It is important, however, to insist that the geographer needs to know the meaning, the explanation, the origin, of the forms that he looks at, simply because of the aid thus received when he attempts to observe and describe the forms carefully. It is necessary clearly to recognize this principle, and constantly to bear it in mind, if we would avoid the error of confounding the objects of geographical and geological study. The latter examines the changes of the past for their own sake, inasmuch as geology is concerned with the history of the Earth; the former examines the changes of the past only so far as they serve to illuminate the present, for geography is concerned essentially with the Earth as it now exists. Structure is a pertinent element of geographical the disuse of imlagination, invention, deduction, and the various other mental faculties that contribute towards the attainment of a well-tested explanation. It is like walking on one foot, or looking with one eye, to exclude from geography the " theoretical" half of the brain-power, which other sciences call upon as well as the "practical" half. Indeed, it is only as a result of misunderstanding that an antipathy is implied between theory and practice, for in geography, as in all sound scientific work, the two advance most amiably and effectively together. Surely the fullest development of geography will not be reached until all the mental faculties that are in any way pertinent to its cultivation are well trained and exercised in geographical investigation.

All this may be stated in another way. One of the most effective aids to the appreciation of a subject is a correct explanation of the facts that it presents. Understanding thus comes to aid the memory. But a genetic classification of geographical forms is, in effect, an explanation of them; hence such a classification must be helpful to the travelling,

.studying, or teaching geographer, provided only that it is a true and natural classification. True and natural a genetic classification may

,certainly be, for the time is past when even geographers can look on the forms of lands as "ready made." Indeed, geographical definitions and descriptions are untrue and unnatural just so far as they give the impression that the forms of the lands are of unknown origin, not sus- ceptible of rational explanation. From the very beginning of geography in the lower schools, the pupils should be possessed with the belief that geographical forms have meaning, and that the meaning or origin of so many forms is already so well assured that there is every reason to think that the meaning of all the others will be discovered in due time. The explorer of the Earth should be as fully convinced of this principle, and as well prepared to apply it, as the explorer of the sky is to carry physical principles to the furthest reach of his telescope, his spectro- scope, and his camera. The preparation of route-maps and the deter- mination of latitude, longitude, and altitude for the more important points is only the beginning of exploration, which has no end till all the facts of observation are carried forward to explanation.

(Parte 1 de 4)

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