BUTE. GEOLOGY. 46l 



rate them effectually; and it is often rather from the 

 predominant characters of the whole series, than from 

 the aspect of any particular portion, that a single term 

 for designating them must be derived. These schists, 

 as they occur in Bute, whether ranked under the one 

 or the other title, present considerable diversity of struc- 

 ture ; but the most marked are those in which the quartz 

 is intermixed with the mica or chlorite in a granularly lami- 

 nar, or in a more continuously foliated manner. 



I may add to this account, that slate quarries are 

 wrought in different parts of the island; no distinction 

 being made among the various substances, but every 

 one being attempted which promises to admit of the 

 requisite mechanical conditions. The principal quarries 

 are about Scalspie and Bannatyne. 



Before terminating this account of the primary rocks 

 of Bute, one remark of a general nature may be made 

 on the nature of the argillaceous series, involving geolo- 

 gical doubts of considerable importance. It must have 

 already appeared in many parts of this work, that no 

 necessary geological distinction exists between gray- 

 wacke schist and common clay slate; while it has also 

 been proved that these rocks occur in alternation 

 with all the other primary strata. Even here, it is seen, 

 that although the clay slate occupies a position near 

 the outer margin of these strata, it is not followed 

 by the graywacke ; but that both substances, even where 

 the series is most simple, are intermixed, so as to form 

 different parts of one general deposit. In this case there- 

 fore, as in many others, there is no geological distinction 

 between the two, which appear, on the contrary, to be 

 different parts of one mass, composed fundamentally of 

 blue indurated clay and quartz, and differing only in 

 the relative minuteness and proportions of these different 

 ingredients. It will be a question for geologists to con- 

 sider, whether the appropriation of the term graywacke 

 to a particular variety of argillaceous schist, does not 



