INDIRECTNESS OP THE CONTRACTION A L IlYrOTllESIS. G9 



the best tlie hypothesis rests on a double inference: the first througli 

 honioh^t^y in the hiboratory, the second through analogy between labora- 

 tory product and natural process. Tliere is no direct line of reasoning 

 in its support, and there remain outstanding the ample and perpetual 

 vertical oscillations of the earthcrust wliich the hypothesis is incompe- 

 tent to explain. 



The ^Ieaning of the Movements. 



Vertical movements in the earthcrust have been recorded and some- 

 times measured by a hundred geologists in different countries, and the 

 formations and unconformities of a score of geologic provinces have been 

 interpreted through homology with observed oscillations by most geolo- 

 gists in every country. Thus there is a vast bod}^ of knowledge concern- 

 ing movements in tlie earthcrust which demand explanation. Partial 

 explanations have indeed been promulgated. Powell and Gilbert, under 

 the inspiration of a magnificent field, have shown that unloaded areas 

 rise and that loaded areas sink, yet this triumph of liomogenic reasoning 

 does not indicate the source of the energy required to perj^etuate the 

 mechanism. Dutton has formulated the suggestive law of isostasy, but 

 it may be questioned whether this law in its simple form is competent 

 to explain the greater oscillations. It has been shown elsewhere that the 

 areas of deposition throughout the world, so far as not complicated by 

 other conditions, are areas of subsidence, and thus that the generaliza- 

 tions oY Powell, Gilbert and Dutton are sustained by present as well as 

 past agencies ; * the corporeal movements of the earthcrust have Ijcen 

 discriminated and grouped as (1) antecedent and (2) consequent,']' and 

 the latter have l)een shown to be governed l)y and the former to tran- 

 scend the law of isostasy; yet the primary corporeal movements of the 

 earth await a consistent and quantitatively adequate explanation.^ 



It is not the purpose to either affirm or deny the validity of the con- 

 tractional hyi)othesis as applied to the abnormal quarter of the land 

 surface of the i)lanet in which the rocks of each age are crumpled and 

 thrust, though it may be suggested that a simpler hypothesis will yet be 

 found along the line long ago suggested by Herschel and more recently 

 developed in connection with the modern displacement of our coastal 

 plain ; § it is the purpose to question, and indeed to deny, the applica- 



* The Gulf of Mexico as a Measure of Isostasy : Am. Jour. Sci., 3d ser., vol. xliv, 1892, pp. 177-192. 



t'Some Definitions in Dynamical Geology : Geol. Mag., Decade III, vol. v, 1888, pp. 489-495. 



X It may be observed that Powell lias for4Tiulated. hut not yet published, an apparently satisfac- 

 tory explanation of these antecedent vertical movements. The author has ottered a tentative 

 explanation (Hull. Minnesota Academy of Sciences, vol. iii, 1888, pp. 191-200), but the adequacy of 

 the cau>«e indicated is open to question. 



g Seventh .\nnual Report of the United States Geological Survey, 1888, pp. G2G-634. 



