462 SCIENCE PROGRESS. 



(1) Whether the Tertiary folds follow the direction of 

 the primary ones, to which they are superposed ? 



(2) Have these folds been formed progressively in con- 

 sequence of continuous, or slightly superadded, movements ? 

 and — 



(3) Whether the system of main foldings is accompanied 

 by one of perpendicular crumpling ? 



The method pursued by him is full of interest, and 

 capable of wider application. Starting on the assumption 

 that the Cretaceous beds have been deposited on an ap- 

 proximately level surface, a plane of marine denudation, he 

 concludes that wherever these overlie the junction of two 

 Jurassic beds that spot must have existed on the junction 

 line when the Cretaceous beds were laid down. Obtaining, 

 therefore, a series of such points over a given area, he is at 

 length able to trace out a map of that district as it must 

 have appeared in pre-Cretaceous times, and the study of 

 such a map reveals the character of the foldings ere the 

 Cretaceous beds were deposited, as also the relations of the 

 outcrop of the Jurassic strata to the approximately hori- 

 zontal surface. Then taking a contoured map of the coun- 

 try under investigation, and obtaining the present height 

 of the base, of the Cretaceous in different localities, it will 

 be seen that it is possible to follow the direction of the 

 ridges and troughs produced by post-Cretaceous move- 

 ments, the result of the application of these methods 

 being to prove the important fact that the post-Creta- 

 ceous folds are exactly superposed on the pre-Cretaceous : 

 this result, the professor believes, will also hold true when 

 the Jurassic and Palaeozoic strata shall have been more 

 closely considered. 



His general conclusion (p. 146) is that folds are always 

 formed on the same spots, and that a general design, marked 

 out already at the beginning of geological time, has presided 

 over the deformation of the earth's crust. 



Our author, however, does not consider that folds alone 

 are sufficient to account for all the varied features of the 

 earth's surface. He is of opinion that, together with them, 

 there are elliptical portions of its crust which undergo eleva- 



