MICHIGAN ACADEMY OF SCIENCE. 137 



down in the progress of the ages, dynamical geology "the treatment of 

 causes, agencies and processes."' 



The factors embraced in the study of physical geography are mainly the 

 atmospheric temperature, the effect of meteoric water, with the resultants 

 of topographic forms, denudation and aggradation. As we have just seen 

 dynamics treats of causes, agencies and processes, which therefore furnishes 

 the nearest correlative in geological science, and it is believed that these 

 two branches are mutually complimentary. 



As a science physical geography antedates that of geology, and was 

 formerly understood as "embracing two equally important and closely re- 

 lated subjects — the interior structure of the globe and its external form."^ 

 James Hutton "started with the grand conception that the past history of 

 our globe must be explained by what can be seen to be happening now, or 

 to have happened only recently. The dominant idea in his philosophy is 

 that the present is the key to the past. The pudding stones were in his 

 eyes only compacted gravels, the sandstones were indurated sands, the lime- 

 stones were in great part derived from the accumulation of the remains of 

 marine calcareous organisms, the shales from the consolidation of mud and 

 silt."^ It is with certain of these agents and resultants that we have here 

 to deal. In this connection I am indebted to Wm. M. Davis, professor of 

 physical geology at Harvard University, for a communication on the sub- 

 ject: 



" I will only say in brief that I regard physical geography, or physiography, 

 as a sub-heading of geography, and treating of all the inorganic content of 

 geograph}^ namely, everything concerning the earth as a globe — the oceans, 

 the air and the lands which go to make up the inorganic environment of 

 organic inhabitants of the earth. Geography as a whole I look upon as 

 simply the geology of today; as I have sometimes expressed it, geography 

 is only today's issue of a world's record, the complete files of which would 

 constitute geolog}^; or, in other words, geography is the top member of a 

 series of strata horizontally arranged with respect to the vertical time line. 

 There has always been a geography, and geology is nothing but a summa- 

 tion of all geographies of the past, up to and including the present. The 

 chief reason that has separated geography from geology so long, and so 

 much to its disadvantage is that the facts of geography are open to imme- 

 diate observation as existing phenomena. The facts of past geographies, 

 which make up geology, are determined only by inference and are known 

 very incompletely. In their essence, however, they would surely be very 

 much like the observable facts of today's geography. It is for this reason 

 that the whole tendency of my work has been to bring out a closer associa- 

 tion of geolog}^ and geography than has been customary in the past. A 

 great deal that is taught in geology, concerning processes now going on, is 

 good physical geography. The bulk of historical geology is (fragmentary) 

 geography of past ages — partly phj'sical, partly organic (ontographic.)" 



" In a sense physical geography is to geology as physiology is to anatomy, 

 the essential element being activity in its effect on geological deposits, as 

 embodied in dynamic agencies. The agents as far as will be considered 

 here, are the water, precipitation, the results and changes of temperature, 

 with certain topographic features. These factors and the dynamic result- 



1 Chamberlin & Salisbury, Geology, Volumn I, p. 1. 



2. "The Principles of Geology", Volume I, A. Geikie, 1901, p. 74. 



3 Idem. p. 168. 



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