68 REPORT— 1839. 



new red sandstone, much obscured by diluvial and alluvial deposits. 

 Gypsiferous beds are exposed at Cotehill and other places. At Broad- 

 field the subjacent carboniferous limestone is brought up and tilted at 

 an angle of at least 40°. Dip south. Commencing at its most western 

 point on the east side of the river Petterell at Petterell's Crook, about 

 six miles south of Carlisle, a columnar mass of globular concentric 

 balls of basalt is seen, which is again exposed on the Penrith road and 

 on the summit of Great Barrock. Continuing this line the dyke is 

 traced at Armathwaite, Combe's Peak, Stony Croft, Cringle Dyke, Ren- 

 wick, Ravenswater, Hartside Fell, and disappears about half a mile 

 south of Tynehead smelting-mill. The length of this dyke is twenty- 

 two miles, its width twenty to thirty yards ; and as its course almost 

 coincides with that of the great Cleveland dyke, the author suggests 

 that it is not improbable that they may be connected. 



On the Geological Horizon of the Rocks of S. Devon and Cornwall, 

 as regards that Section of the great Grauwacke Group comprised in 

 the counties of Somerset, Devon and Cornwall, By the Rev. D. Wil- 

 liams, F.G.S. 



The author first combats the opinion expressed by Mr. Weaver in 

 the Philosophical Magazine, third series, vol. xv. p. 109, that the culm 

 strata of Devon are unconformable to the trilobite slates which un- 

 derlie them. He shows that the two examples of unconformity ad- 

 duced by Mr. Weaver, at Rumson Lane and Muddle Bridge near 

 Barnstaple, are due to local derangement of the strata, and that the 

 general conformity of these two series of rocks is proved by numerous 

 observations in other places. The connecting link between them is 

 the " Coddon Hill Grit," containing elliptical masses of " Posidonia 

 Limestone," and repeatedly alternating with the slate rocks below and 

 the culm strata above, along the north borders of the central trough, 

 and on the south margin abrupted through the plant-bearing beds and 

 the overlying Cornish killas ; its broad anticlinal line thus constituting 

 the southern border, extending from Bos Castle on the sea to the green- 

 sand and chalk-flints of Haldon near Exeter. These Coddon Hill 

 grits, Posidonia limestones and floriferous beds, after repeated alterna- 

 tions and mineral gradations, are eventually overlaid by the slates of 

 Cornwall, — a fact, he states, which is well shown at St. Mellion and 

 Pillaton on the south of Callington, and about Pentilly Castle on the 

 west bank of the Tamar three miles below Calstock, where a good sec- 

 tion of the St. Mellion and Pillaton rocks is exhibited. Mr. Williams 

 refers the whole of the fossiliferous and other slates and limestones of 

 S. Devon and Cornwall to this intermediate part of the series, which 

 he considers to be somewhat older than the old red sandstone and car- 

 boniferous limestone of other parts of England, — a view in which he 

 considers himself fortified by the mountain-limestone type of many of 

 the fossils from the Plymouth limestone. The strata of this region are 



