324 Speciroscojnc Exainination of Silicates. 



In connection with the rehitions of the land shell ftiunas of 

 the islands on the north side of the Caribbean Sea, I may 

 mention that the greatest depth between the coast of Yucatan 

 and Cape San Antonio, the western extremity of Cuba, about 

 midway betvveen the two, is 1,164 fathoms (6,984 feet),* — 

 between the east end of Jamaica and the west end of Haiti 

 (so far as is yet known), 600 fathoms (3,600 feet), and 

 north of Mona Island, in the Mona Passage (between Haiti 

 and Porto Rico) 250 lathoms (1500 feet). I postpone com- 

 parison of the faunas of the islands and the adjacent parts of 

 the North American continent, but in regard to the depth 

 between Haiti and Jamaica on the west side, and Porto Eico 

 on the east it is noticeable, that while the fauna of Haiti has 

 very little relation with that of Jamaica, it has much alliance 

 with that of Porto Rico. 



XXIX. — Speciroscojnc Examination of Silicates. 



By Prof. ALBERT R. LEEDS, 



Stevens Institute of Technology, Iloboken, N. J. 



Read March 10, 1873. 



While conducting the analysis of a silicious mineral, and 

 determining its alkalies by the well-known and universally 

 employed process of Prof. J. Lawrence Smith, which it 

 would be entirely superfluous to repeat here, it occurred to 

 me that a modification of this process would be valuable in 

 the spectroscopic examination of silicates. 



It is evident that a pulverulent mixture of a powdered 

 mineral with sal-ammoniac and precipitated calcic carbonate 



*I am indebted to the kindness ol I'rofesBor Peirce, Superintendent of the U. S. 

 Coast Survey, and of Professor Heni-y, of the Smithsdnian Institution, for full particu- 

 Ivrs of the deep-sea soundings betvveen Cape Catoche and Cape San Antonio, ascer- 

 tained on the survey in 1872. 



