Page:Transactions of the Geological Society, 1st series, vol. 3.djvu/308

 instances to which no distinct denomination bas been applied, as this term of syenite has been to those which contain hornblende. And since the granite of mica, felspar, and quartz, is sometimes found to contain here and there a solitary crystal of hornblende, with which in a series of gradation those varieties in which hornblende at length prevails to the exclusion of the mica are connected, it is impossible to define the point at which granite is to end and syenite is to begin: there is no difficulty in modifying the application of the adjective term. But another, and the principal advantage arises from the limitation of the term syenite to a rock of which the mineral character is much more constant, at the same time that it is in general very strongly distinguished from granite in its appearance. In its geological connections also it differs so widely that it is absolutely necessary to remove all chance of their being confounded together, since this rock is connected with the trap family, and is found in a position in which neither granite nor syenitic granite has ever yet been seen, namely, incumbent on the rocks of secondary formation.

To proceed to the description of the rock at the junctions formerly described. It consists chiefly of high red felspar and white quartz, of which the latter is generally in the smallest proportion, the compound mass containing obscure crystals of dark green hornblende. These are seldom in large quantity, more commonly they are thinly dispersed through the rock, and not seldom even in the largest masses of rock they are altogether absent. I have not observed mica in any of the granite at the junctions described, but in several parts of the hills the same rock, or one not to be distinguished from it except by this circumstance, is found to contain mica together with hornblende, which latter not infrequently becomes excluded altogether and the simplest form of granite remains.