4 i, . . J - . * . * a 
interior of cavities. Viewed in reflected light, by the mucro- 
356 Messrs. Johnson and Blake on Kaolinite and Pholerite. 
and the words of DesCloizeaux, above quoted, appear to be the 
first recorded optical observations on kaolinite. Pisani’s analysis 
is given in the subjoined table. 
Kaolin is described by nearly all writers as an opake amor- 
hous substance. Some have mentioned it to confain minute 
transparent plates, but have supposed them to be sheets of mica 
or other admixture. e have examined microscopically twenty 
specimens of kaolin, pipe- and fire-clay. Most of these are of 
unknown origin. In them all is found a greater or less propor- 
tion of transparent plates, and in the most of them these plates 
are abundant, evidently constituting the bulk of the substance. 
The kaolin from Diendorf (Bodenmais), Bavaria, is perhaps the 
_ most finely divided of all the white clays we have studied. 
When dusted dry upon a glass slide it appears to consist chiefly 
of masses of a white substance that are opake or nearly so in 
transmitted light, but, when fully illuminated above and below, 
have the translucent aspect of snow in the lump. Interspersed 
among these masses may be seen extremely minute transparent 
plates of irregular rounded outline. When brought into water 
the masses are almost entirely resolved into similar transparent 
lates, most of which are not more than ‘0001 of an inch in 
breadth. This description applies to all the finer plastic clays. 
Even the dark-colored Stourbridge clay is made up in large part 
of transparent lamine, as is a compact sedimentary brownish-gray 
pipe-clay from Table mountain, Tuolumne Co., Cal. The same 
is true of the blue fire-clay from Mt. Savage, Md., the white 
clays of Brandon, Vt., Perth Amboy 
especially on one collected at one of the hematite mines at Beek- 
mann, ave observed pearly glistening surfaces on the 
scope, these surfaces were seen to be covered with minute scaly 
erystals, or crystalline aggregates, which, however, revealed no 
regular outlines, : 
A white, pulverulent substance, having much the appearance 
of powd starch or wheat flour, found near Richmond, V., 
was recently analyzed by Mr. Burton in the Sheffield Laboratory. 
Its Saw eget agrees with Forchhammer’s formuld (see below), 
part o 
ma 
in The Sane Lectgnatay 
les are frequently 
lates are rarely 
other. The edges of these bun 
