58 PROCEEDINGS OF THE AMERICAN ACADEMY 



It is evident from these analyses that the atomic ratio of the mineral 

 is 2 : 1 : 1 : 1, and its formula may therefore be written : — 



Jig, R . 0^2 • '^^3 • ^^2 ^' 



By referring to what has already been said of the relation of Jefferi- 

 site to the Biotites, it will be seen that, while that mineral corresponds 

 to a less common variety of this species, the Culsagee vermiculite cor- 

 responds to its more usual type. We give below, at (l),the results of 

 an analysis of Vesuvian Biotite, by Chodnef ; and, at (2), the same, 

 assuming that a portion of the iron is in the ferrous condition, as is 

 well known to be the case, in order to show that values within the 

 probable error of the analysis would give the ratio 2:1:1. Here, of 

 course, the alkali takes the place of a portion of the magnesia of the 

 vermiculite. 



This new variety of vermiculite is so well marked, and the compo- 

 sition so definite, that I have thought best to designate it by the name 

 Culsageeite. As regards its otlier characters, it has a specific gravity 

 of 2.225 (taken in alcohol), and about the hardness of talc. Before 

 the blowpipe the exfoliated mineral fuses readily to a white enamel, 

 but does not fuse in the flame of a Bunsen lamp. 



To this variety of vermiculite belongs, as I have already intimated, 

 the original mineral from Millbury, analyzed by Crossley. There can 

 be no question as to the general accuracy of Crossley's results ; and, 

 assuming that all the iron is in the ferric condition, they give, as I 

 have shown, almost precisely the atomic ratio 2:1:1:1. The only 

 question that can arise is in regard to the condition of the iron. I 

 have therefore made an assay of the iron by the accurate method I 

 formerly described in the Am. Jour. Sci., xliv. 347, 1867. One him- 

 dred parts of the massive mineral gave 7.40 per cent ferric oxide, and 

 3.86 per cent ferric oxide, which corresponds to a total of 10.56 ferrous 

 oxide. Crossley found 10.02 ferrous oxide, but he separated with great 

 care the vermiculite from the steatite with which it is mixed ; and this 

 steatite was probably the source of the greater part of the small quan- 

 tity of ferrous oxide found in our assay, which, though not made with 



