400 ~C. Schuchert — Paleozoic Crustal Instability 



fore he was aware of Chamberlin's work, but was printed 

 three months later. The third, published in 1915, was by 

 Schuchert. 4 



Early in 1917, Blackwelder stated in a letter: "On one 

 thing I think we are all agreed, and that is, that orogenic 

 epochs, or disturbances, or revolutions, or whatever else 

 they may be called, are coming to have due recognition, 

 and that it is inevitable that some system of naming them 

 will be adopted by the geological fraternity." At the 

 present time, the writer offers no complete nomenclatorial 

 scheme, but seeks rather to point out when some of the 

 Paleozoic crustal deformations took place, along with the 

 times of most marked detrital sedimentation, and some- 

 thing as well in regard to the geographic extent of these 

 two sets of diastrophic criteria. 



The structural relief of the lithosphere, or crustal de- 

 formation, is thought to be essentially due to earth shrink- 

 age, and the resulting diastrophism is of two categories. 



(1) The wider and more significant diastrophisms, the 

 negative movements, have in the course of geologic time 

 brought into being the oceanic basins as seen to-day. The 

 continents are therefore for a time left standing as horsts. 



(2) The other type of crustal movement is orogenic and 

 positive, i. e., is mountain-making, folding the continents 

 along narrow belts which are the former sites of geosyn- 

 clines. 



Dana, in the fourth edition of his famous Manual of 

 Geology, 5 says: "The origin of the shape of the earth's 

 mass" is "geogenic work, [and] pertains to astronomy." 

 We would say that it pertains as well to geophysics and 

 geology. He further states that "The origin of conti- 

 nental plateaus and oceanic depressions, and of all move- 

 ments in the earth's crust through geological time not 

 involving orogenic work . . . [has] been termed by G. K. 

 Gilbert epeirogenic, or continent-making." 



Sir Archibald Geikie says, 6 in regard to the deforma- 

 tions : "Major Powell proposed the use of the term 

 i diastrophism' to denote all the processes of deformation 

 of the earth's crust. Elevation, subsidence, plication, 

 and fracture are all diastrophic. Mr. Gilbert 7 has fur- 



4 Pirsson-Schuchert Text-book of Geology, 1915. 



6 Dana, J. D., Manual of Geology, 4th ed., p. 376, 1895. 

 a Text-book of Geologv, 4th ed., p. 392, 1903. 



7 Gilbert, G. K., U. S. Geol. Survey, Monog. 1, pp. 3, 340, 1890. 



