chap, x.] CONTINUITY OF THE CHALK. 517 



From 1,263 Fathoms (Station 22). 



A single rounded pebble, weighing 18 grains, chiefly quartz, 

 with a little of a black mineral hornblende or tourmaline, prob- 

 ably from a metamorphic schist. 



Gravel from 1,366 Fathoms (Station 19«). 



Consisted of 51 small subangular pieces of rock, all less than 

 \ grain in weight, excepting only one fragment (angular) of 

 quartz, which weighed 2 grains ; they consisted of — 



19 Fragments of quartz, all of which appeared to have pro- 

 ceeded from the disintegration of crystalline schists, and 

 not from granite. 



9 Hornblende schist. 



8 Mica schist. 



7 Loose, dirty-white tufaceous limestone. 



3 Small fragments of augite or tourmaline (? which). 

 1 Fragment of quartz, with tourmaline. 



4 Fragments of indistinct and uncertain character. 



51 



Gravel from 1,476 Fathoms (Station 21). 



Six small subangular fragments, the largest of which did not 

 exceed two grains in weight ; they were respectively — 



1 Yellow quartz. 



1 Quartzose chlorite schist. 



3 Mica schist. 



1 Small fragment, apparently of volcanic lava. 



6 



The specimen from Rockall is not a fragment of any normal 

 rock, but is only a brecciaform aggregate, principally consisting 

 of quartz, felspar, and crystals of green hornblende, held to- 

 gether by a silicious cement. It has evidently been broken 

 from the projecting edge of a fault or vein fissure ; and although 

 it cannot settle the matter definitely as to what rocks this islet 

 may really be composed of, it would indicate that it most 



