Rev. J. F. Blake — Form of Sedimentary Deposits. 75' 



But if, with Godwin-Austen, we account for tlie absence of 

 Jurassic rocks over a wide area east of London, not by the area 

 being too far from land, but by its being •' dry land at this period," 

 then the western side has been subsequently elevated, and the slopes 

 which now are south-easterly were once north-westerly. We also 

 have a proof that thicker beds as a whole correspond to deeper water, 

 and that the original form of a sedimentary deposit as here described 

 is the true one. 



It is interesting to note what a difference in questions of palaso- 

 geography this interpretation of the form of a deposit makes. If 

 we take Professor Hull's view, perhaps the most commonly accepted 

 one, we read this general conclusion : " During the deposition of the 

 Upper PalEeozoic and Lower Mesozoic rocks an extensive tract of land 

 existed to the north-west of the British Isles which afforded the 

 materials of which these rocks are composed." ^ If, on the other 

 hand, we take the view here put forward, apparently assumed but 

 not definitely enunciated by Godwin-Austen, we are led to the 

 conclusion that " The Oolites of Yorkshire and Lincolnshire were 

 dependent on a land which Iny to the east," ^ and to the extension 

 of this land on the map as far as the line of the North Downs.^ 



We may now test the supposed form of a sedimentary deposit by 

 its effect upon the submarine contours. We have seen that this 

 form involved the occurrence of a markedly rapid slope in the 

 sea-bottom, corresponding to the seaward termination of the deposits. 

 This slope might be at .various distances from land, and affect 

 various contour-lines, but more especially that of 100 fathoms. 



In the case of the banks of coarser deposit in shallow depths, it is 

 easy to see examples in the edges of the parallel roads of Glenroy, or 

 in the undisturbed banks in dried-up lakes ; and Godwin-Austen * 

 states from actual survey that in the English Channel " the 

 termination of deposits of a well-defined character, such as the 

 shell-gravel beds or those of clean sand, is often by slopes more 

 or less steep." Such banks and slopes, however, from being com- 

 paratively small and in shallow water, are easily altered by or 

 confounded with the results of transverse currents. 



It is, however, with the more extensive slopes which may mark 

 the limit of deposits formed from sediment in suspension that we 

 are most concerned. Possibly Godwin-Austen's observations apply to 

 some of these deposits, as he compares them with escarpments of such 

 when raised above sea-level, but in any case the great slope now 

 referred to as the 'continental slope' has been known {fide G.-A.) 



1 Hull: op. cit., p. 8. 



2 Godwin-Austen: Q.J.G.S., vol. xii, p. 64. 



^ Since this paper was read at Belfast, I have received the 21st Annual Report of 

 the U.S. Geol. Survey, with an account of the Cretaceous formation of Texas by 

 E. T. Hill. A full account is therein given of the thickening seaward of the 

 Glen Eose formation (see pp. 138-9 and 3G9-382). This has been preserved from 

 denudation by the overlying Fredericksburg Division, and is bounded below by the 

 PaliBozoic rocks. Its thickening is observed in artesian wells. It has thus retained 

 its original form, which is ' wedge-shaped,' but the termination seaward I cannot 

 find described. 



* Q.J.G.S., vol. vi, p. 79. 



