60 W J MCGEE — UNIFORMITARIANISM AND DEFOEMATION. 



kind aione ; the formations are like the observed products of submer- 

 gence, the unconformities are like the observed products of running waters, 

 the movements inferred are like the movements observed, and thereby 

 the danger of error in interpretation is greatly reduced, if not entirely 

 eliminated. So the record of the coastal plains is in harmony with obser- 

 vation on subsiding coasts and with direct inferences from uplifted 

 strands— it is a record of corporeal movement within the earthcrust which 

 is chiefly or wholly vertical, only subordinately if at all horizontal. 



MOVEMENTS INFERRED FROM THE CONTINENTS. 



Throughout an area of some 150,000 square miles in eastern United 

 States, comprising the Appalachian and Piedmont regions, the Adiron- 

 dack dome, and the New England hills, as well as throughout areas 

 of perhaps 50,000 miles in the Lake Superior region and 25,000 square 

 miles in the Ozark region, the rocks are strongly contorted and more or 

 less metamorphosed. Throughout an area of about 125,000 square miles 

 on the Pacific slope, including the Coast range and the Sierra, together 

 with the Klamath and other mountain systems, the rocks are similarly 

 deformed, and throughout a gross area of perhaps 150,000 square miles, 

 embracing the Rocky mountain region and certain Basin ranges, the 

 strata are in large part affected by flexures and thrust faults. There is 

 thus an aggregate area of some 500,000 square miles, or one-sixth of the 

 territory of the United States (exclusive of Alaska), which may be charac- 

 terized as mountainous and in which the strata are flexed, thrust-faulted, 

 and otherwise deformed in a manner similar to that in which smaller 

 bodies are deformed by horizontal compression. This is the geologically 

 aberrant fraction of our territory, the relatively small area in which the 

 structure is exceptional and abnormal. 



Throughout an aggregate area of perhaps 250,000 square miles, embrac- 

 ing much of the Great basin, with parts of the Columbia mesas on the 

 north and the High plateaus on the south, the surface is submountainous 

 and the strata are broken up into great tilted blocks bounded by normal 

 faults. The deformation in this twelfth of our territory is explicable 

 only as the product of predominantly vertical movement with a subordi- 

 nate horizontal element in the direction of extension, and this inference 

 is in accord with experience of movements similar in kind to those in- 

 ferred in the Lone Pine and Sonora earthquakes. This is a partially 

 aberrant fraction of the country in which the movements recorded in the 

 rocks are normal in kind though exceptional in degree. 



Throughout the remaining three-fourths of the United States the strata 

 represent a succession of formations and unconformities analogous to 



