DIASTROPHISM AND THE FORMATIVE PROCESSES 269 



built out, they serve as a causeway on which the topset beds are 

 advanced seaward. 



The finer element embraces those portions of the silts from the 

 land that were light enough or fine enough to be kept in suspension— 

 or to be stirred up frequently into temporary suspension — by the 

 agitated waters of the shelf-seas and so borne oceanward continu- 

 ously or by stages. They were, however, insufficiently comminuted 

 to float long and so to reach the central ocean areas and find lodg- 

 ment in the true abysmal depths. This element in general is inter- 

 mediate between the coarser flotation material which settles and 

 remains on the sea-shelves in spite of considerable agitation, and 

 the extremely fine silt that reaches the heart of the ocean and enters 

 into the deep-sea deposits. 



The many obvious qualifications of these broad statements need 

 not detain us here for we are seeking chiefly the relations of these 

 formative processes to problems of diastrophism. The matter of 

 first special interest in this relationship concerns the thicknesses of 

 the foreset, the topset, and the flotation beds respectively and the 

 inferences drawn from these thicknesses. It is common practice to 

 regard the thickness attained by any series of beds prior to a defor- 

 mation, as a measure of the subsidence of the crust, if evidences of 

 agitated water or shoal life occur at various horizons in the series. 

 This inferred subsidence, when large, is often thought to have 

 invited a deformative movement. Theories of the cause or of the 

 localizing agency of deformations have been hung on such supposed 

 proof of deep subsidence. Appeals have been made to a rise of the 

 geotherms supposed to be consequent upon subsidence. Even 

 softening or melting of the under crust has been deduced from such 

 depression. When the series is thick and shows abundant evidence 

 of^shallow-water action at nearly ah horizons, these features have 

 been regarded as proof of such deep subsidence, and the proof has 

 been felt to be quite irrefragable. Few tenets of geology have a 

 firmer hold on the convictions of working geologists or have seemed 

 more nearly axiomatic. If the trustworthiness of this tenet is to 

 be called in question, in any sense, or in any degree, the grounds 

 for so doing should be clear. 



Flotation beds may be laid down in strict horizontality, and on 



