Rev. J. F. Blake — Form of Sedimentary Deposits. 79 



of the La Plata, opposite the mouth of which the chart accompanying 

 the Summary of Kesults of the Challenger Expedition shows a broad 

 seaward deflection of the 2,000 fathom line. It is, of course, very 

 difficult to assign every peculiarity of a contour to its proper cause, 

 but in this case there is no remarkable submarine bulge along the 

 whole eastern coast, except where theory would lead us to expect it. 

 In the north coast there is also a longer bulge, corresponding to the 

 Amazon, but driven westward by the equatorial cui-rent. 



If the differences of depth near coastlines are due to the deposition 

 or non-deposition of sediment, we might expect that where long-shore 

 currents do not interfere the lateral boundary of a deposit should 

 also be marked by a slope, and the interval between deposits from 

 different sources by a broad channel. In this way we may suggest 

 a reason for such peculiar features as the ' Fosse du Cap Breton,' 

 ' the Baltic Kiver,' and the ' Swatch of no ground.' The first 

 of these may be the interval between the deposits from the Loire 

 and Gironde and the slopes of the Pyrenees, where there is little 

 deposit ; the second, between the wide and ancient deposits which 

 have covered the North Sea from the Elbe, Ehine, Thames, etc., 

 and the almost unaltered boundary of South Norway ; and the third, 

 between the deposits reaching the Indian Ocean by way of the 

 Hoogly and by way of the Brahmaputra respectively. 



The views here propounded may now, I think, claim to be supported, 

 not only by a priori arguments, but by many undeniable facts of 

 nature of which they offer an explanation, and by several first-hand 

 observers who have been led to adopt some part of them at least, 

 as occasion served. But they are subversive of common assumptions 

 in so far as these are applied to uniform deposits, and they alter 

 entirely our means of interpretation of the sources of any stratum. 

 The ' continental slope ' has been called an escarpment, though 

 the term was afterwards withdrawn ; but according to these views 

 it is an escarpment, but with this difference : it is an escarpment yet 

 to be. When the marine deposits have been raised above sea-level 

 and we stand facing the escarpment, we may be looking at the 

 actual end of the deposit, except for later weathering backwards, 

 and we must look along the present dip slope towards the land 

 whence the material of the strata has been derived. 



When limestones give place along the strike to clays we must not 

 look for the shore in that direction, but in a direction perpendicular 

 thereto, nor must the sea be supposed to have been deeper beneath the 

 limestone, but possibly shallower, the unevenness of the sea-bottom 

 having caused the clays to be deposited elsewhere. 



Neither must we regard the existence of a well-marked continental 

 slope as a proof of depression, it may be of 6,000 feet or less, of 

 a land of great mobility ; but look on it as a proof of stability, 

 which allowed the slowly deposited sediments to retain the same 

 limit for so long a time. The existence of the continental slope 

 in this way speaks against the hypothesis of a glacial submergence. 



On the other hand, we must be careful not to push theoretical 

 results beyond their proper limits. Deposits may be altered in 



