20 Original Articles. [Jan., 



sandstones, and conglomerates which go to form the Triassic and Per- 

 mian formations of the central counties, as also the Liassic, Oolitic, and 

 Cretaceous groups of the eastern and southern counties, is one of the 

 most interesting problems which it is the province of the geologist to 

 solve. It is, in fact, a compound problem, embracing several questions 

 concerning the physical geography of our island before, during, and 

 after the formation of the coal-measures* themselves. It was once 

 supposed that all the formations from the coal-measures upwards 

 succeeded each other with such regularity and persistency, that when- 

 ever one group was found at the surface all the earlier groups were 

 certain to occur beneath. More recent observations, however, have 

 tended to dispel this illusion, and to show that the Carboniferous rocks 

 have been deposited over certain ever-widening depressions more or 

 less bounded by tracts of land which never were submerged during the 

 whole period ; and that as regards the Carboniferous groups themselves, 

 and those which succeed them, they are to be regarded not as a series 

 of heterogeneous strata deposited without plan, in some places more 

 thickly than in others, without the possibility of determining where 

 the thickness may be greater or less, but as a series of wedge-shaped 

 layers lying one over the other along certain well-determined bearings 

 of the compass. These conclusions lead us to note some remarkable 

 coincidences in the physical geology of Great Britain, upon which we 

 shall touch at the conclusion of this paper. 



The subject naturally divides itself into four heads : — 



1. Nature of the floor over which the Carboniferous strata were 



originally spread. 



2. The distribution of the Carboniferous strata themselves. 



3. The distribution of the formations which overlie the Carboniferous 



strata. 



4. The mutual relationship of these formations, and their teachings. 



In treating on these subjects I shall avail myself of the views 

 expressed by several writers on the physical geology of our islands, to 

 whom once for all I beg to express my acknowledgments. f 



1. Tlie Nature of the Floor and Original Margin of the Carboniferous 



Strata. 



The rocks which precede in point of time the Carboniferous are 

 referable to three great systems — the Cambrian, Silurian, and Devo- 

 nian ; and it would seem that at the close of each of the last-named 

 periods in the north of England and Wales, the rocks were upheaved 

 into islands, or it may be into land which was continuous over the 



* The term " coal-measures" is that generally used to denote the upper Carboni- 

 ferous rocks which eontain the principal beds of coal in England ; they consist 

 principally of shales, clays, and sandstones of various kinds formed in the sea. 



f Amongst others I would specially refer to Professor Phillips (' Geology of 

 Yorkshire ') ; Professor Sedgwick (" Memoirs on the Formations of the North of 

 England," 'Geological Transactions'); Mr. Jukes C Memoir on the South Staf- 

 fordshire Coal-field ') ; Mr. Godwin-Austen (' Quarterly Journ. Geol. Soc.,' vol. xi.). 

 Some of the points in this paper have been treated of by myself more fully than 

 space will allow of here, in two Memoirs in the 'Journ. Geol. Soo.,' vols. xvi. and 

 xviii. 



