492 



On the Scientific Exploration of the Deep 8ea. 



" From 1263 fathoms (Station 22)." 



A single rounded pebble, weighing 18 grains, chiefly quartz, with a little 

 of a black mineral hornblende or tourmaline, probably from a metamorphic 

 schist. 



" Gravel from 1366 fathoms (Station 19a)." 



Consisted of 5 1 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 proceeded 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 1476 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 together by a siliceous 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 probably is 

 a mass of hornblendic gneiss or schist, and certainly not of true volcanic 

 origin. I may mention that it does not at all resemble any of the frag- 

 ments found in the deep-sea dredgings which I have as yet examined. 



