ITS CHEMICAL CHARACTERS. 187 



serpentine, lie almost entirely between 2.00 and H.OO. This decrease in 

 specific gravity is generally accompanied with a diminution of the rehitive 

 ferruginous contents, and an increase in that of the magnesia. 



It was observed in the pallasites that only one contained over 30 per cent 

 of silica, while it may be seen here that only three of the Iherzohtes fall 

 below that percentage, and one of these is a carbonaceous meteorite which 

 contains considerable organic matter and water. Another of these analvses 

 is considered to be worthless. In the mention of the chemical analvses, 

 reference, as a rule, is had to the first one when more than one is given for a 

 single locality ; for when several analyses are available, that one is placed 

 first which is thought to be the more nearly correct, judging by the analyses 

 and the analyst, when any especial difference exists. Of course, no such 

 differences in composition occur in the same specimen, as some of the given 

 analyses displaj^, and many of these are poor and unreliable. 



Only two of the analyses show for peridotite a higher percentage than 

 47 per cent — St. Paul's Rocks 47.15, and the Cabarras meteorite 56.168. 

 This meteorite has in general been assigned to the basaltic division of the 

 meteorites ; but since, macroscopically, it has the characters of the peridotites, 

 it has here been placed with them, in the belief that some error exists in the 

 published analysis. It is to be hoped that a microscopic examination and 

 further chemical analyses will be made of the Cabarras stone. 



Only two meteoric and three terrestrial peridotites have a percentage of 

 silica above 45, and below 47, per cent. One of the meteorites has two 

 analyses in which the silica is respectively 46 and 48.25 per cent, made by 

 Higgins in 1811. Had the second analysis been placed first, then the above 

 statements would have varied accordingly. 



From the above it can be seen that out of 193 different peridotites 

 analyzed, all but 11 have their percentage of silica lying between 30 and 45, 

 while the vast majority are included between 33 and 43 per cent. The 

 meteorites preponderate in the lower percentages — the terrestrial rocks in 

 the higher ones. 



Except in the case of the picrites there cannot at present be said to be 

 any gradation in the percentages of silica, according to the variety, from 

 dunite up to picrite, although a tendency towards some arrangement lias 

 been observed. Of course, the more nearly the rock approaches to a purely 

 olivine one or to a pure serpentine, the more nearly the percentage of silica 

 will correspond to the typical analyses of those minerals. 



