and the schist are stratified rocks. I have observed the same appearances in clay slate, and they are frequent in the islands of Scarba and Jura, where this substance alternates with quartz rock, and where great contortions of these rocks have occurred. A more remarkable example occurs in a rock which constitutes one of the numerous beds of which Schihallien is composed. This rock is a micaceous schist, containing imbedded fragments of granite and of quartz rock, often of considerable magnitude. The larger fragments of quartz rock are sometimes partially split at right angles to its laminar structure, and these fissures are filled with the substance of the mica slate, putting on the same pseudomorphous appearance of a vein. I have found similar veins of red sandstone in the limestone of Arran, and they have also been seen in trap. But in a paper on Kinnoul I have described and delineated a specimen from a very extensive set of appearances of this nature, where a schist of the graywacké character becomes prolonged into ramifying veins in the interstices of a trap rock by which it is broken and disturbed. It is unnecessary therefore to enter on the subject in this place, but it will be sufficient to say that such pseudomorphous veins must be considered as portions of the strata, which, during their soft or softened state have been forcibly compressed and elongated into that form. The appearance occurring at Schihallien might obviously be produced by the mica while in a loose state in water, falling into and occupying the open spaces of the fragments deposited with it; and, in a similar manner, rifts in limestone might have been filled by the loose sand which formed the surrounding strata. The explanation of the other circumstances which occur at the junction of the limestone and hornblende schist which has given rise to these remarks, will be as obvious to those who shall inspect
Page:Transactions of the Geological Society, 1st series, vol. 3.djvu/288
