hereafter to he described, and the crystals thus seem to be imbedded in a mass of cotton.
The size of the crystals varies from that of a pin's head to the diameter of half an inch; but in general they present only one modification, the twenty-four sided crystal with trapezoidal faces, of greater or less regularity. The only other form which I found was the primitive, and of that I procured but two specimens, while a ship might be loaded with the trapezoidal variety. The crystals described are sometimes opake and white, at others they are mottled with a mixture of opake and transparent parts, while in a third, but less common case, they are transparent. In this latter case, when minute, they sometimes transmit the black colour of the subjacent basalt to which they adhere, so perfectly as to resemble a velvety surface of black crystals. In similar circumstances, transmitting the greyish or ochry colour of the substance to which they are attached, they appear to possess a colour which a more narrow inspection shows to be fallacious. A few specimens however occur of a flesh red, a colour frequently found in almost all the minerals of this family, and very predominant in the different zeolites which occur at Glen Farg in Perthshire. I also found a solitary specimen. of a pale sea green colour, but did not observe that variety of a pale bluish grey, which, in company with the flesh coloured and yellow green, I have seen in the rocks at Larne in Ireland.
Chabasite is found in similar circumstances on the same shore, but it is comparatively of very rare occurrence: it abounds however in the rocks at the Storr, which for a considerahle space consist of an amygdaloid containing it accompanied by stilbite. It is here so common, occupying cavities of greater or less magnitude, that a, fourth or fifth part of the total bulk of the rock is sometime constituted by the chabasite.