

BUTE. GEOLOGY. 459 



ture, but occasionally also, crystalline and large grained ; 

 the colours being either smoke grey or white. 



With respect to the general order of these several rocks 

 in the series, it is the following. The micaceous and 

 chlorite schists prevail near the series of micaceous schist 

 which precedes the argillaceous series ; but are not exclu- 

 sively limited to that part, since the latter in particular, 

 are intermixed with the clay slate, and extend, even be- 

 yond it, to the borders of the secondary strata. The 

 former is also frequently found in the same situation ; so 

 that the clay slate, which in a general sense may 

 be said to occupy the middle of the belt, is sometimes 

 included within the micaceous schist. In some parts 

 of the line already so often alluded to, the graywacke 

 schists prevail near the borders of the series, so as to 

 come into contact with the secondary strata; and this 

 appearance takes place to a considerable degree in Bute. 

 But in many others, no such distinction is to be observed ; 

 the fine clay slate being found alternating throughout with 

 the coarser or graywacke schists, even to the very borders 

 of the sandstone. That mixture is often so intimate that 

 both substances exist even in the same specimen ; not 

 even an alternation of the several beds occurring, but 

 the same lamina frequently presenting both structures. 

 In other cases, beds of the clay slate occur among those 

 of the graywacke, being extenuated at their sides into thin 

 edges ; and, in a similar manner, the latter rock is found 

 imbedded in the strata of the former. In terminating 

 these remarks on the nature of this series, it is not unim- 

 portant to point out the strong resemblance in structure 

 between the graywacke and the coarse varieties of 

 micaceous and of chlorite schist. In all, it is precisely 

 the same ; the difference consisting only in the nature 

 of the cement. 



The different rocks that have thus been enumerated 

 as belonging to this series, do not all occur throughout 

 the whole line where it is found ; nor are the inter- 



