English Stratified Rocks below the Old Red Sandstone, fyc. 1 49 



of protruded masses of granite. It is generally made up of beds of 

 a hard arenaceous greywacke, sometimes of a very coarse structure, 

 sometimes finer, and occasionally passing into a good roofing slate, 

 — generally it is without fossils ; but the Graptolites foliaceus (first 

 noticed by Mr. Carrick Moore) occurs, though rarely, among the 

 finer slates. In these respects the chain is analogous to that in 

 Pembrokeshire, where the same fossil occurs in the slates below the 

 Lower Silurian rocks of Mr. Murchison. 



He then notices a ridge of rocks visited by Mr. Carrick Moore 

 and himself, which breaks out from under the carboniferous basin of 

 Girvan- water in Ayrshire. It contains many fossils, among which 

 Mr. Sowerby finds three or four new species of Orthis, Tentaculites, 

 Atrypa, and one or two species of Terebratula. Near it, and probably 

 forming a part of it, is a small mass of limestone, with many corals 

 and some Trilobites, the latter unfortunately lost by the author. 

 Mr. Lonsdale states that the corals are difficult and obscure, but 

 there is a true Favosites fibrosa, probably also a Favosites spongites ; 

 and there are, among the specimens, several small hemispherical 

 corals which may be young Stromatopora concentrica. From this 

 evidence he would be inclined to refer the limestone to an Upper 

 Silurian or Devonian group. From the number of Orthidia, Mr. 

 Sowerby would refer the fossiliferous slates to the Lower Silurian ; 

 but the whole mass, including slates and limestone, is of small extent, 

 and seems to form but one group, which maybe considered as Silurian. 



To show the position of these beds, the author gives a transverse 

 section from the Solway Firth over the Galloway chain to the fossil 

 group above mentioned. The groups on the section appear in the 

 following order, beginning at the south end : — 1. Old red sandstone. 

 2. Greywacke of the Galloway chain. 3. Granite. 4. Greywacke 

 of the Galloway chain on the north side of the axis. 5. Unconform- 

 able masses of old red sandstone. 6. Coal-basin of Girvan- water. 

 7. Fossiliferous slates and limestone rising from under the coal series. 



Conclusion. — It appears, from the preceding synopsis, that there is 

 a continuous and apparently uninterrupted sequence of deposits 

 from the lower beds of the new red sandstone formation to the low- 

 est known strata of England ; that beds of masses of limestone ap- 

 pear here and there in the descending series ; and (with the excep- 

 tion of the mountain limestone) that they are neither so continuous 

 nor so fixed in their place as to offer any good bases for the general 

 classification of the groups ; that the divisions into which the de- 

 scending series may be separated often pass into one another, so as 

 to make their demarcations doubtful or arbitrary; and that, in the 

 lower divisions, organic remains gradually disappear. The great di- 

 visions of the descending series hitherto ascertained are as follows : — 



1. Carboniferous. — Passing in some places at its upper limits into 

 the lower new red sandstone. 



2. Old red sandstone. — Passing in its upper limits (Scotland and 

 Ireland) into the first division, and including the slate rocks, &c, of 

 Devon and a part of Cornwall. 



3. Silurian. — Passing in its upper groups into the old red sandstone . 



