677 



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 cliass, 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 

 that have brought up a portion of the older rocks (of the class here 

 described) at Dudley, on both sides of the Warwickshire coal field, 

 and in Charnwood forest. At all these localities the strike is the 

 same, and the lines of greatest movement are nearly parallel — all being 

 about N.N.W. and S.S.E. ; and all these movements belong to one 

 epoch, having been completed after the deposition of the lower red 

 sandstone, and before the period of the upper and gypseous marls. 

 Hence we have three great systems of elevation, each marked by 

 parallel lines of strike, and the three systems of strike indicating 

 three distinct periods of elevation. 



The author then points out the importance of such facts to the 

 broad speculations of geology, as well as the limitations under which 

 they are to be applied. The dynamical powers of elevation appear 

 to have been employed in three principal forms. 1st. In gradually 

 raising up ridges through large spaces of the earth's crust. These 

 will explain the correspondence of strike through very extensive 

 regions ; and such elevations if continued beyond a certain limit must 

 have produced longitudinal fissures and lines of volcanic vent. 2ndly. 

 In the long-continued protrusion and eruption of igneous rocks along 

 such lines of vent. 3dly. In local and partial eruptions and pro- 

 trusions, producing valleys of elevation, local derangements, and other 



3 l2 



