Page:Transactions of the Geological Society, 1st series, vol. 3.djvu/40

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slate and quartz rock as unstratified, but their want of regularity in the present instance, compared with the extreme precision and order of those which follow, render the distinction convenient here for the temporary purpose of describing them. I have in other instances produced sufficient examples of the alternate and regular stratification of quartz rock and mica slate to render it unnecessary to say more on that subject: I have in the same places shown that these rocks alternate with clay slate, and my object at this moment is to distinguish strongly the sudden change from great disturbance to extreme regularity, which takes place here between two rocks which in so many other instances seem to have undergone together the common action of some disturbing force.

The first of these rocks is a compound series of beds consisting of dark blue quartz rock interlaminated with thin layers of clay slate of the same colour: these are to be found in immediate contact with the white quartz rock, and in an order which is conformable to the general position of that substance where it is in contact with them. Often the quartz of this rock prevails to the total exclusion of the schist, and the beds are then much thicker than when the schist interferes. They hold a remarkably even and straight course I for a considerable space on the north side of Loch Eishort, dipping to the N.W. at an angle of about 80°. The thickness of this set of beds appears to be extremely variable, but I know not that it can be ascertained, since the excavation which forms Loch Eishort interferes with the observation at the western point of their exposure, as the sea in that place covers the elevated edges, while in their course eastward they become clothed with the covering of soil. There is consequently a chasm in my attempt to trace their extent eastward, but as the same rock appears on the eastern side with all the same characters, and in the same position with respect