Page:Transactions of the Geological Society, 1st series, vol. 1.djvu/95

 Rh the other on their ends. This structure, if I may be allowed the comparison, is like the bud of a flower, in which the form of the petals cannot be seen except by tearing it open and unfolding them. May it not be the same in many other substances which occur also in fascicular masses of more or less considerable size, such as tourmaline, thallite, prehnite, analcime, stilbite, &c. May not also the irregularity of the interior of these masses be at the same time owing to the difference in the variety of forms which these aggregated crystals present? and if it were possible to separate in these masses each of the component crystals, with as much facility as they are separated in the masses of the laumonite, might we not obtain the same result?



There is a striking irregularity in the manner in which the planes of substitution are situated on the laumonite, an example of which may be seen in fig. 3, with respect to those by which the edges of 92° 80′, in the prism are replaced. The same irregularity occurs in the position of the planes which are the result of the other modifications; for example, in the crystal delineated in fig. 28, there occurs in the place of one of the two obtuse angles of the terminal faces, a plane belonging to the 9th modification, whilst the plane of substitution for the other angle belongs to the 8th. In fig. 30. there exists a still greater irregularity in the planes of substitution of these two angles, one of them being replaced by two planes, which belong to the 8th and 9th modifications, and the other by a single plane of the 10th. This fresh example, if it were necessary, might serve to shew the difference which exists between the retrogradations on primitive crystals, where the geometrical form is one in which all the pants are perfectly symmetrical, and those on primitive crystals, in which the parts are not so circumstanced. A symmetry is established between