May, 1922 dynamics of the lithosphere 201 



assumed. The computed density subtracted from the observed 

 density gives an anomaly which is approximately 1 part error 

 and 4 parts departure in density from the normal. When 

 observed density is less than the computed density the anomaly 

 is negative. The anomalies thus secured bear no relation to 

 topography. 



The following conclusions have been pointed out: 



1. The anomalies bear no definite relation to loading and 



unloading. 



2. The United States is in isostatic adjustment with a mean 



departure of 171 m. of rock with 2.67 density. 



3. A relation to geologic formation exists by which the 



older formations have a positive anomaly. 



4. Intrusive and effusive rocks give an anomaly very near 



to complete and perfect isostatic compensation. 



DATA OF DIASTROPHISM.23 



It is hardly necessary to review here the evidence of actual 

 crustal movement. One might, however, mention a few of the 

 most important, such as mountain making, folding, faulting, 

 tilting of lakes, elevated or depressed shorelines with their 

 familiar accompanying physiographic features, actual measure- 

 ment of movements, and submergence of oceanic islands. 

 There was much change of level in and after the Pleistocene 

 in the Great Lakes region, in Scotland, and in Scandinavia. ^'^ 



The most noticeable fact of diastrophism is that it is most 

 intense in regions of thick sedimentation, that is, where geo- 

 synclines have been filled. The Appalachian geosyncline 

 presents 12,000 meters of sediment; others have nearly as great 

 thickness; 10,000 meters are found in the Laramide structure; 

 3,000 meters of Eocene rocks were deposited in the Rocky 

 Mountain geosyncline. The Alps present 15,000 meters of 

 sediment. 



Experiments reveal an expansive coefficient of 1 cm. to 19.2 

 meters for every rise of 100° C. in average rock. In the case 

 of the Appalachians, 800° at the bottom of the geosyncline 

 would have given 1650 meters expansion. In Pennsylvania 



23The most satisfactory discussion of the facts and theories of this problem is 

 found in Dana's Manual of Geology, fourth edition. 



2nV. B. Wright: Quaternary Ice Age, 1914, pp. 406-426. 



