2 BRITISH CARBONIFEROUS BRACHIOPODA. 



made up of a vast accumulation of beds of limestone, shales, indurated clays, grits, 

 coal and sandstone, alternating to a large extent ; and which may in different districts 

 or countries be more or less successfully divided into two, three, or even four principal 

 groups, viz. : 



1. The Coal measures (the uppermost bed of which lies under the Lower New Red 



Sandstone of the Permian series) are composed of a vast accumulation of 

 beds of clay, shale, coal, and sandstone, divided more or less by layers of 

 ironstone and chert. These beds intercalate with each other, and at times also 

 with — 



2. The Millstone grit, which underlies the Coal measures properly so termed. It is 



chiefly composed of a coarse-grained, gritty sandstone, not very dissimilar in 

 character from the one found above, but it also alternates with many beds of 

 limestone, shale, and even coal, and presents some of the features of — 



3. The Carboniferous or Mountain Limestone. These large bands of hard limestone 



principally prevail in the Yoredale and Scar Limestones of Yorkshire, but they 



are likewise interstratified with beds of grits, &c. ; the series being terminated 



by lower Carboniferous shales and sandstones, which at times assume a red 



colour. 



But the basement line of the Carboniferous system is still a subject of some divergence 



in opinion, as certain geologists would comprise within its limits all or portions of the 



Old Bed Sandstone, while others consider the strata last named to form part of the Devonian 



system. 1 



1 In a most interesting memoir, entitled * Researches among the Palaeozoic Rocks of Ireland,' pub- 

 lished in the seventh volume of the 'Journal of the Geol. Soc. of Dublin' (1856), Mr. Kelly is a 

 strong advocate for the admission of what he terms the Old Red Sandstone into the Carboniferous system, 

 and even seems doubtful as to the propriety of admitting the Devonian system in total. It must, 

 however, be here remembered that Mr. Kelly founds his views chiefly on appearances peculiar to Ireland ; 

 he also refers to statements made by Dr. M'Culloch (in his 'Treatise on Geology,' 1831), and to the 

 table published by Professor Phillips, at p. 1 1 of the * Geology of Yorkshire,' in which the learned 

 Professor divides the Carboniferous system into three principal parts — the Coal formation, the Carboni- 

 ferous Limestone, and the Old Red Sandstone, — adding at the same time that "the Carboniferous system 

 does undoubtedly permit itself to be considered in three series, characterised by the prevalence of coal, 

 limestone, and red sandstone." Mr. Kelly then states that the Carboniferous formations of Ireland 

 are likewise divisible into a similar triple system, which he seeks to develop in his valuable memoir, to 

 which we must refer the reader for more ample details. It may, however, be observed that bands of red 

 sandstone no doubt occur and form part of the Carboniferous group, but it remains to be a question 

 for further consideration whether the Old Red Sandstone of the Devonian period should or not, in part 

 or in total, be considered as a portion of the great Carboniferous system? Sir R. Murchison kindly 

 informs me that there exists in Ireland a series of many thousand feet of shales and grits, &c, above the 

 highest Upper Silurian, with all the characteristic fossils, and which represents precisely in time the 

 mass of the Devonian rocks ; and that, from his last year's direct survey of Ireland, his belief is that the 

 Old Red system, Devonian, in Ireland, has undergone a great separation into two parts, which has not 

 occurred in England or Scotland. Professor De Koninck seems also inclined to admit a portion of the 



