SUBMARINE DEPOSITS. 271 



ites, mica schists, serpentine rocks, and compact limestones. These 

 fragments were not larger than six or seven centimetres in diameter. 

 The 'Blake,' in 1,241 fathoms, and Lat. 39° 43' N., dredged large frag- 

 ments of the same rocks, some of which were glaciated. In Lat. 41° 

 14' N. and 1,340 fathoms the ' Challenger ' again dredged similar rock 

 fragments, and one block of syenite weighing five hundi'ed-weight. 

 These deposits being all within the influence of the Labrador current, 

 these rocks may be regarded as chiefly ice-borne. The mineral par- 

 ticles ^ and clayey matter usually make up from eightj' to eighty-five 

 per cent of the whole deposit. 



" The carbonate of lime in these deposits varies from about three to 

 eighteen per cent ; it consists of coccoliths and coccospheres, of pelagic 

 and other foraminifera, and of fragments of echinoderms, polyzoa, ostra- 

 codes, and mollusks. The jielagic foraminifera shells and coccosi^heres 

 are more abundant in the deeper deposits far from the land than in 

 those from shallower water near the coast. 



•' The siliceous remains of diatoms, radiolarians, and sponges, to- 

 gether with arenaceous foraminifera and glauconitic casts of calca- 

 reous foraminifera, make up sometimes four or five per cent of the 

 deposit. Mixed with the mud are also found pinnules of crinoids and 

 otoliths of fishes." 



Mr. Pourtales noticed, from his examination of the large col- 

 lection of foraminifera brought together in the soundings made 

 by officers of the Coast Survey, that off our Atlantic coasts cer- 

 tain forms of foraminifera characterized distinct regions. 



" The first, nearest the coast line, is marked by a great poverty of 

 forms. Excepting a few small Polystomellae, we find nothing in the 

 sand, which is kept in continual motion by the waves. This region 

 may be considered to extend to a depth of ten or twelve fathoms. 

 Farther seaward there are cUfferent species of Miliolinae, but not in 

 large numbers. They extend to about forty fathoms, and also beyond, 

 as it were sporadically. . . . 



" From twenty-five to seventy fathoms Triincatullna advena D'Orb. 

 is the characteristic form. The next region, that of the larger Margi- 

 nulinse and Cristellariae, encroaches on the first ; it begins at a depth 

 of about thirty-five fathoms, and extends one hundred fathoms be- 

 yond. . . . 



" From a depth of sixty fathoms the sand begins to be mixed with 

 Globigerinae, their numbers increasing so much with the depth that at 



1 The mineral particles consist of frag- hornblende, augite, mica, tourmaline, and 

 ments of ancient rocks, quartz, mono- occasionally glauconitic grains, 

 clinic and triclinic feldspars, magnetite, 



