§2. THE DEVONIAN SYSTEM. 751 



ceals for ever the earliest scenes of the earth's physical 

 drama. 



2. The Devonian System. — I purpose in this division 

 of the present Lecture to consider the characters and rela- 

 tions of the three remaining systems of fossiliferous deposits, 

 namely, the Devonian, Silurian, and Cumbrian : all the 

 rocks of more ancient date, so far as our present knowledge 

 extends, being destitute of any traces of organization, whe- 

 ther of the animal or of the vegetable kingdoms. 



The Devonian system, formerly called the Old Red Sand- 

 stone (ante, p. 204), lies immediately beneath the Carboni- 

 ferous limestone, and is largely developed in Devonshire, 

 Herefordshire, Monmouthshire, &c. : and in the south-east 

 border of the Grampians, and over the whole of the northern 

 part of Scotland. It consists of many alternations of con- 

 glomerates, shales, and sandstones, in various states of indu- 

 ration. The sandstone is often of a schistose character, 

 and this variety is largely employed for roofing, under the 

 name of tilestone. The conglomerates are formed of quartz 

 pebbles, waterworn fragments of slate and other rocks, 

 cemented together either by an argillaceous or a siliceous 

 paste, coloured, more or less, of a deep red, by peroxide of 

 iron. These strata have evidently resulted from the degra- 

 dation of ancient slate rocks; for they are entirely made up 

 of pebbles, sand, and mud, accumulated in depressions of 

 the bed of the sea. The mountains of Scotland are bor- 

 dered by immense deposits of a like character ; and those of 

 North and South Wales by red pebbly sandstone. Some 

 eminent geologists are of opinion that prior to the formation 

 of the Devonian deposits, the Cumbrian slaty group of 

 sands, flag-stones, &c, with porphyritic conglomerates, had 

 been long consolidated ; and that they were subsequently ele- 

 vated by subterranean movements, and thrown on edge, and 

 formed an irregular island ; and at the same time parts of 

 the Grampians, Lammermuirs, and the slaty districts of 



