1 50 New South Wales. pake i. 



slope from the coast very gently towards a certain line* 

 in the offing, beyond which the depth in most cases sud- 

 denly becomes great. I may instance the great banks 

 of sediment within the West Indian Archipelago, 1 

 which terminate in submarine slopes, inclined at angles 

 of between 30 and 40 degrees, and sometimes even at 

 more than 40 degrees : every one knows how steep such 

 a slope would appear on the land. Banks of this nature, 

 if uplifted, would probably have nearly the same ex- 

 ternal form as the platform of the Blue Mountains, 

 where it abruptly terminates over the Nepean. 



Current cleavage. — The strata of sandstone in the 

 low coast country, and likewise on the Blue Mountains, 

 are often divided by cross or current laminae, which 

 dip in different directions, and frequently at an angle 

 of forty-five degrees. Most authors have attributed 

 these cross layers to successive small accumulations on 

 an inclined surface ; but from a careful examination in 

 some parts of the New Red sandstone of England, I 

 believe that such layers generally form parts of a series 

 of curves, like gigantic tidal ripples, the tops of which 

 have since been cut off, either by nearly horizontal 

 layers, or by another set of great ripples, the folds of 

 which do not exactly coincide with those below them. 

 It is well known to surveyors that mud and sand are dis- 

 turbed during storms at considerable depths, at least from 

 300 to 450 feet, 2 so that the nature of the bottom even 

 becomes temporarily changed; the bottom, also, at a 



1 I have described these very curious banks in the Appendix 

 (2nd edit. p. 255) to my volume on the structure of Coral Reefs I 

 have ascertained the inclination of the edges of the banks, from 

 information given me by Captain B. AUen, one of the surveyors, and 

 by carefully measuring the horizontal distances between the last 

 sounding on the bank and the first in the deep water. Widely ex- 

 tended banks in all parts of the West Indies have the same general 

 form of surface. 



2 See Martin White, on * Soundings in the British Channel,' pp. 4 

 and 166. 



