280 Dr. Mac CuLLOCH o« //&^ Geology of Glen Tilt. 



stone 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 conslder.ible 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 delineared 

 a specimen from a very extensive set of appearances of this 

 nature, where a schist of the graywacke character becomes pro- 

 longed 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 



