106 Gregory — Progress in Interpretation of Land Forms. 



the 19tli century. Hutton's "Theory of the Earth, with 

 Proofs and Illustrations/' in which the guidance of 

 DeSaussure and Desmarest is gratefully acknowledged, 

 appeared in 1795. The original publication aroused only 

 local interest, but when placed in attractive form by Play- 

 fair 's "Illustrations of the Huttonian Theory" (1802), 

 the problem of the origin and development of land forms 

 assumed a commanding position in geological thought, 

 Hutton was peculiarly fortunate in his environment. He 

 had the support and assistance of a group of able scien- 

 tific colleagues as well as the bitter opposition of Jameson 

 and of the defenders of orthodoxy. His views were 

 discussed in scientific publications and found their way to 

 literary and theological journals. Hutton's conception 

 of the processes of land sculpture — slow upheaving and 

 slow degradation of mountains, differential weathering, 

 and the carving of valleys by streams — has a very 

 modern aspect. Playf air's book would scarcely be out of 

 place in a 20th century class room. The following para- 

 graphs are quoted from it : 3 



" ... A river, of which the course is both serpentine and 

 deeply excavated in the rock, is among the phenomena, by 

 which the slow waste of the land, and also the cause of that 

 waste, are most directly pointed out. 



The structure of the vallies among mountains, shews clearly to 

 what cause their existence is to be ascribed. Here we have first 

 a large valley, communicating directly with the plain, and wind- 

 ing between high ridges of mountains, while the river in the 

 bottom of it descends over a surface, remarkable, in such a 

 scene, for its uniform declivity. Into this, open a multitude of 

 transverse or secondary vallies, intersecting the ridges on either 

 side of the former, each bringing a contribution to the main 

 stream, proportioned to its magnitude; and, except where a 

 cataract now and then intervenes, all having that nice adjust- 

 ment in their levels, which is the more wonderful, the greater 

 the irregularity of the surface. These secondary vallies have 

 others of a smaller size opening into them; and, among moun- 

 tains of the first order, where all is laid out on the greatest scale, 

 these ramifications are continued to a fourth, and even a fifth, 

 each diminishing in size as it increases in elevation, and as its 

 supply of water is less. Through them all, this law is in gen- 

 eral observed, that where a higher valley joins a lower one, of 

 the two angles which it makes with the latter, that which is 

 obtuse is always on the descending side ; . . . what else but the 

 water itself, working its way through obstacles of unequal 



