Geology and Mineralogy. 225 



the deposits vary with the kinds of coasts; and beyond 100 fath- 

 oms, they are still determined largely by the greater or less prox- 

 imity to he embouchures of rivers or to coral reefs. Throughout 

 the region the mineral particles (not calcareous) seldom exceed 

 - l mm in size and they appear to be wholly derived from the 

 rivers of the continent. The calcareous portion consists mostly 

 of pelagic Foraminifera and shells of Mollusca. In depths be- 

 yond 2000 fathoms, Pteropod and Heteropod shells appear to be 

 nearly if not quite absent, the calcareous material being Forami- 

 niferal ; but in less depths they are common; and between the 

 200 and 500 fathom lines, they make in many places the chief 

 part of the deposits. In some places the deposits are chalk-like. 

 Of Radolarians and sponge spicules, only three per cent. 



In the Florida Straits there are interesting phosphatic concre- 

 tions. In one Mr. Klement found 33*42 per cent of phosphoric 

 acid, with 5 - 80 carbon dioxide, 2-74 sulphur trioxide, 51*90 of 

 of lime, magnesia 0*70, iron and alumina 1*56, fluorine 1*21, insolu- 

 ble residue 0*21, loss on ignition 2*16, with traces of silica and chlo- 

 rine. The presence of so much fluorine in this and the other con- 

 cretion analyzed by Mr. Klement is an interesting fact. Mr. 

 Murray observes that " that there are difficulties in understanding 

 how calcium phosphate and calcium carbonate are deposited at 

 the bottom of the sea, yet there is no doubt that such a deposi- 

 tion does take place under some special circumstances. Their 

 solution in the ocean water is an almost universal phenomenon." 



2. Tornebohm on the formation of quartzite by enlargement 

 of the quartz fragments of sandstone / by R. D. Irving. — In 

 recent publications on this subject (Bulletin No. 8, U. S. Geo- 

 logical Survey, and Fifth Annual Report, U. S. Geological Sur- 

 vey) I have attributed to Sorby the first recognition of the process 

 of enlargement of quartz fragments, which we now know to have 

 been well nigh universal in quartzose fragmental rocks ; while at 

 the same time showing that several others, including myself, had 

 independently observed such enlargements. Recently my atten- 

 tion has been drawn to the existence of a paper by Tornebohm 

 dating as much as three years before that of Sorby, in which an 

 account is given of a red quartzite from Dalecarlia, Sweden, 

 formed by this process of enlargement from a sandstone. This 

 paper (Geol. Forens. i Stockholm Forh., iii, 21V), the original 

 of which I have not yet been able to see, is reviewed in the Neues 

 Jahrbuch fur Mineralogie for 1877, p. 210; and the statements of 

 the reviewer, evidently reproducing those of Tornebohm, read 

 very like some in my own publications. After saying that the 

 thin section, as seen in ordinary light, shows the fragments 

 . sharply outlined by oxide of iron borders, the reviewer says that 

 in the polarized light, "the borders of the fragmental grains are 

 hardly any longer recognizable ; the rock appears as though it 

 were a crystalline aggregate of irregularly angular quartz grains, 

 exactly fitting one another, just as is the case with the quartzites 



Am. Jotje. Sci. — Third Series, Vol. XXXI, No. 183. — March, 1886. 

 15 



