1869.] On a Ternary Geological Classification. 367 



Carboniferous Series. — The threefold division of this group 

 with its calcareous central member in Great Britain has already 

 been so fully alluded to, that it is scarcely necessary for me to add 

 to what I have already written. I may, however, here remark 

 that although there is a nearly continuous and uninterrupted 

 sequence in the beds from the lower limestone shale throughout, 

 there are both in England and Scotland occasional slight breaks, 

 denudations, and unconformities, but that these are of an excep- 

 tional character, and of limited extent. I have already mentioned 

 my reason for placing the upper " Old Eed Sandstone " of Scotland 

 at the base of the Carboniferous series of that country. 



Permian Series. — It is almost superfluous to insist upon the 

 threefold classification in the case of this group, as originally 

 established by Sir Eoderick Mm-chison and Professor Sedgwick, 

 in the north-east of England, and more recently developed in Lan- 

 cashire and Cumberland by the labours of Professor Harkness, Mr. 

 Binney, and others. Having already described the relations of 

 these beds (see page 361), I shall only here refer to what I consider 

 to be the true position of the Lower Permian rocks of central 

 England and Shropshire with reference to those of the north of 

 England. Those who are famihar with the aspect and physical 

 characters of the Permian beds in these two districts cannot fail to 

 have observed that they belong to two diflerent and distinct types. 

 And regarding as I do the beds of central England and Shropshire 

 as belonging exclusively to the Lower Permian series, the most 

 probable explanation of the difference in their mineralogical 

 characters, as compared with their representatives in the north 

 of England, appears to be that each group was deposited in 

 a separate hydrographical basin, disconnected by a barrier of lower 

 Carboniferous rocks which crossed from west to east under the 

 central plain of Cheshire and parts of South Derbyshire. Into 

 the evidence of the former existence of this barrier I have fully 

 entered in a paper read before the Geological Society of London 

 in 1869. 



Triassic Series.— It is scarcely necessary to observe that in 

 Britain we have no representative of the central calcareous member 

 of tliis natural group. The reasons for the absence of the Mus- 

 chel-kalk and St. Cassian limestones, which on the Continent form 

 the central calcareous member of the group, is now clearly under- 

 stood. In England the basement-beds of the Keuper division rest, 

 with a shght discordance, upon an eroded surface of the Bunter, 

 representing a gap in geological time during which the English 

 area was elevated into dry land, and only submerged again at the 

 commencement of the Keuper period. I regard this case of the 

 Trias of England, bereft of its middle calcareous member, as a 

 parallel case to that of the Devonian group of Wales, Scotland, and 



