ARGILLACEOUS SCHIST. 347 



111 Jura and the connected isles, it forms a 

 triple series with quartz rock and micaceous 

 schist, occurring in very thin beds and in fre- 

 quent alternations ; and, on the adjoining main 

 land, in many places, chlorite schist and lime- 

 stone are superadded to this series. 



In the line which forms the Highland boun- 

 dary to the southward, it occurs in a similar way 

 in a very irregular manner ; the different varieties 

 being intermixed with chlorite and micaceous 

 schists, as also with limestone and minute beds of 

 gneiss. The island of Bute presents this series 

 in great perfection. 



The stratification of argillaceous schist admits 

 of no question, however difficult it may often be 

 to trace the beds. They are sometimes extremely 

 irregular in their forms and disposition, and they 

 vary very much in dimension. Where they al- 

 ternate with other rocks in the manner last des- 

 cribed, they are often very thin ; but where they 

 occur in extensive tracts and unmixed, they attain 

 to such a thickness that it is frequently impos- 

 sible to discover the places where they are sepa- 

 rated. In this respect they present the same dif- 



