516 THE DEPTHS OF THE SEA. [CHAP. x. 



from granite ; the largest of the two fragments weighed 

 15 grains. 



5 Quartz, milky in colour or colourless ; the largest of these 

 weighed 90f grains, and showed evidence of having been 

 derived from the quartz-veins so common in clay-slate. 



19 Fragments of true volcanic lava, most of which were very 

 light and scoriaceous (vesicular), although some small 



38 ones were compact and crystalline; and in these the 

 minerals augite, olivine, and glassy felspar (Sanadine) 

 could be distinctly recognized. Among these were frag- 

 ments of trachytic, trachydoleritic, and pyroxenic (basaltic) 

 lavas, quite similar to those of Iceland or Jan May en 

 of the present period, from which they had probably 

 been derived. 



GRAVEL FROM 1,443 FATHOMS (STATION 20). 



This sample of gravel consisted of 718 subangular fragments, 

 in general not above from J to J grain in weight, with occasion- 

 ally some of a little greater size ; but the most considerable of 

 all (a fragment of mica schist) only weighed 3 grains. They 

 consisted of : 



3 Fragments of orthoclase felspar. 



4 Bituminous or carbonaceous shale (? if not accidental). 



5 Fragments of shell ^indistinguishable species). 



4 Granite, containing quartz, orthoclase, and muscovite. 

 15 Grey compact limestone. 

 69 Quartzose mica schist. 



317 Hornblende schist; sometimes containing garnets. 



273 Quartzite fragments, with a very few fragments of olenr 



quartz. The majority of the pieces being of a dirty 



colour, often cemented together, were evidently the debris 



of quartzite rocks or beds of indurated sandstone, and 



not from granite. 



28 Black compact rock, containing augite, most probably a 



- volcanic basalt. 



718 



