Page:Transactions of the Geological Society, 1st series, vol. 3.djvu/409



Between the blocks which constitute the great mass of rock, a compact substance of a greyish white colour, consisting of an assemblage of crystalline spiculæ diverging from centres, is found. The same compact fossil occurs in the body of the rock, where there has been no rent. This I found to be compact tremolite. This substance assumes also another appearance of distinct and separate crystallization. Crystals of it occur in the fissures of the rock, in a state of promiscuous and thick aggregation. They are about three-fourths of an inch in length, at the longest; and consist of thin, tabular, rectangular prisms, the angles of which are, for the most part, rounded off, so that the section of the prism appears to approach to a long ellipse. Some of these crystals possess a vitreous lustre, and are semitransparent. In general their surface is dull, as if from the effect of weathering, and they are of a brownish ash colour resembling axinite.

Before the strong flame of the blowpipe, a fragment of a crystal melts into a greyish enamel. At the temperature 69. Fahr. I found the specific gravity of these crystals to be 3.20.

I shall not trespass upon the time of the Society by recording the minute detail of chemical experiments. I shall simply state the mode of analysis which I pursued, and the final result of it, so that I may furnish others with the means of judging whether I am warranted in calling this mineral substance a tremolite. The proportions of the several constituent parts of this fossil are given according to an average taken from 100 grains of the distinct crystals.

Acids produce very little effect upon the powdered crystals. No effervescence was produced to indicate the presence of the carbonic acid; neither could I detect any other acid as a constituent ingredient, by means of fusion with pure carbonat of potash, neutralizing