CHAr. yi.] TRICHINOPOLY DISTlilCT OOTATOOR GKOUP. 105 



evidenced by the gradual extension of the grits and conglomerates of 

 the upper beds to the Southward* 



The hypothesis of banking by marine currents accords perfectly 



Amount of dip not ^^®^^ ^^^^^^ ^^^® jDhenomena of strike and dip as 

 discordant with this view, regards direction ; but before we can consider this 

 hypothesis warranted by the factS; it is necessary to assure ourselves that 

 the amount of the dip is in no case greater than may fairly be attributed 

 to this mode of accumulation, I find, on reviewing my notes, that except 

 at the base of the group, where the bottom beds sometimes rest at an 

 angle of 45° on the highly inclined surface of the gneiss, the highest 

 dip I have observed was one of 30°, and that only in one spot. 

 The grit beds in the neighbourhood of Shutanure are those which 

 have the highest continuous dip, and it there averaged 20° increasing 

 in some spots to 25° but this high dip did not prevail beyond 

 a mile or a mile and a half, and is the only instance of the 

 kind met with. Angles of 8°, 10° 12° and 15° are prevalent 

 throughout the group, and with these dips the beds are frequent- 

 ly continuous for one or two miles, both along and across the 

 strike, except, in the case of the bottom beds, which, as I have 

 stated, are, on the W'hole, very irregular. Now the highest of the 

 above dips (30°) is less by 10° than the observed inclination of banks 

 of sediment in the West Indian Archipelago-f- and is also less than 



* Mr. Darwin has shown that although marine currents have not under ordinary circum- 

 stances sufficient force to drift pebbles along the sea bottom, yet that pebbles are widely dis- 

 tributed oyer sub-littoral sea-bottoms. In explanation of this fact he adopts a suggestion of Pro- 

 fessor Play fair's, that the undulations of the sea during heavy gales may have power to lift 

 loose bodies of no great size at considerable depth. His observations show, however, that such 

 movements can take place but rarely, and we might therefore expect that the accumulations 

 of a bank formed by a current bringing down fine and coarse sediment mingled, would at some 

 distance from shore contain but few bands of conglomerate in proportion to the other 

 materials. 



f SeeDavwin, " Observations on Volcanic Islands, &c.," page 133, and the Appendix to the 

 " Structiu-e of Coral reefs," by the same author, page 196. The observations are founded on 

 information afforded to the author by Captain B. Allen. 



O 



