Page:Transactions of the Geological Society, 1st series, vol. 3.djvu/299

 since it must be esteemed an essential character of gneiss that the mica should possess an arrangement, at least so far parallel, as to give the appearance of a foliated structure.

As whatever view we can take of this occurrence is followed by important consequences, it is necessary to consider it somewhat more particularly, and I shall first examine that case in which the gneiss is found alternating with the schist. We have already seen in numerous instances, that great anomalies take place in the aspect of the schistose rocks, as well as of the limestone, wherever they approximate to the granite and are traversed by granite veins, I must therefore premise that no such veins are seen in this place. The mass of granite is here indeed removed to a considerable distance, and the schistose beds are perfectly straight and undisturbed.

The general series consists of mica slate, alternating in a very irregular manner with hard argillaceous schist and quartz rock; and with a few beds of limestone. With these beds is found that micaceous schist which contains felspar, and which will probably be considered by most observers as a modification of gneiss. If then it be called gneiss, that rock alternates with quartz rock, clay slate, mica slate, and limestone, an anomaly at variance with the almost universally received doctrines respecting precedence in rocks. If we now turn our attention to those specimens which have the granitic aspect, I may remark that, however decided this character may be in some particular points about this place, I shall here lay no stress on it, as better examples can be adduced from the hills at no great distance. Although the granite, in the instances which I shall enumerate, occupies but a small space among the laminæ, its texture is perfectly granitic, and bears not the slightest resemblance to that of gneiss, since the mica is placed in all directions, and the portion in question, if detached from the neighbouring parts, could not be