English Stratified BocJcs inferior to the Old Red Sandstone, 301 



(1.) The primary class (composed of gneiss, mica slate, quartz 

 rock, &c. &c.,) is largely developed in the Highlands. 



(2.) The second class (greywack6, greywackd alate, &c. &c,,) is 

 also largely developed in the Lammermuir hills, and in the whole 

 chain extending in the south of Scotland from St. Abb's Head to 

 the Mull of Galloway. It is shown, partly on mineralogical cha- 

 racters, and partly on the evidence of sections, that the rocks of the 

 former class are inferior to those of the latter. For a zone of slate 

 rocks (the roches chloriteuses et quarizeuses of Dr. Boue) is superior 

 to the crystalline slates of the Grampians, and is (at least pro- 

 visionally) placed on the same parallel with the earthy and me- 

 chanical slates of the Lammermuir chain. Both the preceding classes 

 are shown to be inferior, and generally unconformable, to the old red 

 sandstone ; which in the northern part of Scotland was once grouped 

 with the primary class ; but in the geological map of Scotland is now 

 jiut in its true place. 



After giving a series of sections to connect the structure of the 

 Lammermuir chain with the adjacent parts of the north of England, 

 he then proceeds to describe, in general terms, the expansion of the 

 rocks of the second class through various mountainous tracts of 

 South Britain. The frontier chain of Scotland — the slaty series of 

 the Cumbrian mountains — of North and South Wales — and of the 

 whole region between the eastern side of Devon and the western end 

 of Cornwall — as well as the slate rocks of some smaller unconnected 

 tracts, are all referred to one great class, the highest group of which 

 passes into the old red sandstone, while the lowest (where the de- 

 velopment is complete) rests on the crystalline system of the first 

 class. Independently of the direct evidence from detailed sections, 

 the several regions are shown to be related ; 1st, by a common phy- 

 sical structure ; 2ndly, by organic remains ; 3dly, by common lines 

 of strike ; tending to show that several disconnected tracts of wide 

 extent, having partaken of the same accidents, were once probably 

 connected and continuous deposits in a deep sea. 



In illustration of these views he shows that the prevailing strike 

 of the beds (as well as the prevailing direction of the anticlinal and 

 synclinal lines) in the Lammermuir system, in the Cumbrian system, 

 and in the system of all the highest chains of North Wales, is nearly 

 N.E. and S.W. and he further shows that the actual impress was 

 given to all these regions before the period of the old red sandstone. 

 In Cornwall the average strike is about W.N.W., but gradually 

 bends round- to the E. and W., in which prevailing direction the 

 rocks cross Devonshire. In the southern parts of the slate regions 

 of South Wales the beds also have an east and west strike ; and 

 these parallel dislocations of Devonshire and South Wales are pos- 

 terior to the carboniferous series and probably contemporaneous with 

 one another. Where the two preceding systems of strike meet, the 

 beds are thrown into inextricable confusion ; and on the outskirts of 

 Wales, and in the counties where the Silurian system has been most 

 largely developed, the dislocations are too irregular and complicated 

 to be reduced to any law. Lastly, he notices a system of dislocations 



