TRANSACTIONS OF THB SECTIONS. 76 



was not sucli great contortion and denudation previous to the deposition of the 

 basement-bed of the Carboniferous rocks. The patchy sedimentary base, consisting 

 of sands and conglomerate, rests on the Denbigh grits and flags. Skipping the 

 region of mid Wales, we find in South Wales still less pre-Carboniferous crumpling 

 and denudation. As pointed out above, higher beds belonging to the Silm-ian series 

 are left than any seen further north ; and the sedimentary base of the Carboniferous 

 Ls thicker. Still further south (in Devonshire &c.), though the actual base is no- 

 where seen, we have the sedimentary series more strongly developed ; and the early 

 t^'pe of Devonian fossils agrees with the idea that the Devonian area went down 

 first at the commencement of the Carboniferous epoch. 



Uth Epoch. Carboniferous. — In accordance with the above view of the pre- 

 Carboniferous geographical changes, the author, while disagreeing with Prof. 

 Jukes in his interpretation of the stratigraphical structure of Devonshire, still goes 

 with him in bracketing the Devonian with the Carboniferous, and would refer to 

 the same age most of the Old Red of Scotland, while a great portion of the Old 

 Red of South Wales he would group with the Silurian. Running over the principal 

 subdivisions of the Carboniferous, and noticing the occun-ence of coal-seams at 

 lower and lower horizons as we proceed from S. to N., the author next drew at- 

 tention to the large masses of rock of Carboniferous age which had been so deeply 

 stained from the overlying New Red that they had been gi-ouped with that forma- 

 tion ; and pointed out that as we approach the newest known beds of Carbqniferous 

 age, we find indications of the commencement of earth movements in the local 

 irregularities in the sequence of the uppermost Coal-measnres. 



\'2th Epoch. The Ititerval hettveen the Carboniferous and New Red.- — This he con- 

 sidered the second most important gap in the geologic series. The geographical 

 changes which occurred in it were the hardening and upheaval of the whole of the 

 Carboniferous (and how much besides we have not evidence to show), the carving- 

 out of these rocks into hill and valley, and the development of a flora and fauna 

 difiering considerably from those preserved in the Carboniferous rocks. As the 

 base of the New Red rests on the edges of rocks from one to four miles in thick- 

 ness, this epoch must have been of very long duration. 



\Zth Epoch. Neiv Red and Jurassic. — This epoch, like the Carboniferous, com- 

 menced with the variable deposits accumulated along the shores and in the lakes 

 and valleys of an irregular continent unequally submerged. They consist of con- 

 glomerates, sandstones, and mudstones, and, like those at the base of the Carboni- 

 ferous, generally of a bright red colour. The red stain penetrates deep into the 

 underlying rocks, the siu-face of which often shows evidence of subaerial wea- 

 thering. What wonder that, as headlands disappeared, as barriers went down, as 

 depressions got silted up, there should be irregularities of all kinds observable 

 between successive deposits — such, for instance, as that at the base of the Upper 

 Magnesian Limestone in places, or that between the Lower and Upper New Red, 

 or that between the Bunter and Keuper. (He dropped the word Permian, as it 

 was only a new name given by Murchison to what had been previously correctly 

 described by Sedgwick as Lower New Red.) 



These rocks passed up through the Rhfetic and Lias into the Oolitic series, at 

 the close of which, as in every other case, we have a hint of the approaching 

 changes. Probably we shall some day have sufiicienj data to speculate on the limit 

 to which it is possible that continuous deposition can go on uninterruptedly in the 

 same area. However that may be, the further on we get in geologic history the 

 more clear does the evidence become that, as great waves of depression pass across 

 an area, sometimes the accumulation of sediment keeps pace with it, and leaves depo- 

 sits which show that the hollows had been tilled and lagoons and estuaries had taken 

 their place by the time the trough of depression had passed and the wave of upheaval 

 had succeeded. Towards the close of the Jurassic epoch, at any rate, we have the 

 Purbeck freshwater beds, and later the Weald estuary, where we know there had 

 been hundreds, and probably thousands of feet of continuous marine deposits. 



The author then considered briefly the gaps which occurred at the base of the 

 Neocomian and of the Cretaceous, and the intervals of which we have evidence at the 

 base of the Eocene and of the IMiocene, but reserved the fuller investigation of these 

 points for a future occasion. 



1875. 7 



