132 NEW YORK STATE MUSEUM 



and Scandinavia incline to the view that this close uniform folding 

 is to be explained by a uniform contraction of the entire earth crust 

 which then had a fairly homogeneous composition. The influence 

 of enormous masses of eruptive material as an additional factor 

 in the folding is generally recognized, as is also the fact that the 

 folding, foliation, schistosity and longitudinal direction of the 

 intrusive masses (notably the batholiths) are all expressions of 

 the same deformative and compressive forces, all having the same 

 trend lines. 



Suess (v. 3, pt 1, p. 7) has repeatedly emphasized the fact of 

 the contrast between the worldwide Precambrian folding and the 

 restriction of the present folding to local areas of more recent sedi- 

 mentation and therefrom concluded (v. 3, pt 2, p. 720) that while 

 once the lateral pressure due to contraction of the earth was active 

 over the whole planet, it is now localized. 



Among American authorities (see ■ " Problems of American 

 Geology ") it is held that toward the close of the Archeozoic era a 

 period of worldwide diastrophism ensued, which led to the profound 

 folding of the Preproterozoic complex ; and that several such orogenic 

 revolutions followed thereafter in Precambrian time. Geologists are 

 further agreed that these orogenies are probably due to periodic 

 earth shrinkages (Schuchert, 1920, p. 401); but no longer, since the 

 discovery of the fact that the earth is radioactive, consider the earth 

 as a cooling body, but in agreement with Chamber lin's planetesimal 

 theory one seeks the cause of shrinkage in other physical and chemical 

 changes within the earth. Chamberlin (1920) has shown, by 

 deducing the order of magnitude of shrinkage of the earth from 

 Mars, Venus and the Moon, that the total shrinkage of the earth 

 is greater than that of the other bodies adduced for comparison 

 corresponding to the progressive nature of the compression from the 

 least to the greatest, and he was the first to originate the idea that 

 shrinkage originated in the deeper portions of the earth under the 

 urgency of the enormous pressures by giving rise to slow recombi- 

 nations of matter into denser forms. Geologists agree that this 

 shrinkage due to condensation deep within the earth is the principal 

 cause of the profound compressive forces that have been the chief 

 agents in developing mountain structures, and Chamberlin (1920, 

 p. 14) points out that the total shrinkage of the earth has been very 

 large, and likewise that of Precambrian and especially of Archean 

 time. It is estimated (Schuchert, 1918, p. 48) that the diameter of 

 the earth " at the close of the growing period must have been 200 

 and possibly even 400 miles greater, for it is well known to geolo- 



