192 ARGILLACEOUS SCHIST. 



precludes all possibility of a separate stratification. In 

 reality, this and the similar facts noticed all through 

 this work, imply the whole theory of the primary strata, 

 as rock species, distinguished from the secondary ones. 



As argillaceous schist forms extensive tracts, it is 

 easy to study the characters which it confers on a di- 

 strict. In these, there will be found considerable va- 

 riety, as in North Wales, Cumberland, Cornwall, and 

 the South of Scotland. Of these, Snowdon attains a 

 considerable elevation, as does the mountainous tract 

 of Cumberland ; often presenting faces of naked rock, 

 with a variety of rnggedness equalling that of micaceous 

 schist, as in Snowdon, and Langdale pikes, while in 

 Skiddaw and elsewhere, the smooth conoidal and low 

 rounded form more generally characteristic of this rock 

 prevail; as well as in Wales, widely, in the Isle of Mann, 

 in Cornwall, and in the South of Scotland ; though, in 

 Cardiganshire, it is disposed in sudden hills of small 

 elevation, marked by frequent protuberances. And as 

 it generally decomposes readily into a clay, of different 

 degrees of tenacity, it presents a great variety of soils, 

 favourable both to agriculture and to the growth of 

 wood. Its cecononical uses are well known. 



Metalliferous veins occur in both the leading varie- 

 ties of this roek. The tin and copper veins of Corn- 

 wall are common to the schist and the granite, and it 

 necessarily therefore contains the other metals men- 

 tioned under that head. In Scotland, it forms the great 

 mine of the Lead-hills ; and, in other countries, it 

 includes silver, copper, zinc, and more rarely, cobalt, 

 .and gold. 



