Page:Quarterly Journal of the Geological Society of London, vol. 25.djvu/271

 On the other hand, the evidence which I am about to adduce seems to show that the Permian rocks both of the North-west and Northeast of England were disconnected during their deposition from those of the midland counties and Shropshire. Under this view, it will be apparent that there are in reality only two types of Permian beds in England, those of the north and those of the midland counties ; though at first sight it might have been supposed there were three, namely, those of the Salopian, Lancashire, and Durham or Yorkshire types.

Possible Causes of the typical differences in the the Permian formations over the Salopian and Lancashire Areas.

Having thus described the distinctive characters and range of the two types of Permian beds in the tract of country under investigation, it now remains to inquire into the causes of this diversity of character. As already stated, there appear to be three possible modes of explanation.

1. We might suppose that the beds of both types had been deposited in the same basin, and that the differences in mineral and stratigraphical character were due to differences in the sources of the sediment. This explanation appears to me insufficient, as there are no intercalations on either side. Considering the great thickness which this rock attains in North-east Cheshire (at least 1500 feet), and the proximity of the two districts, it is strange that it should not be represented by interstratification amongst the beds of North Staffordshire, if the two areas were in communication, or, on the other hand, that the beds of the Salopian type should not be represented by interstratification amongst those of the Stockport and Manchester district. This explanation also fails to account for the absence of the Upper Permian beds of Lancashire in the southern area, a series of beds which, from their very nature, may be presumed to have extended as far as the hydrographical boundaries would admit.

2. To suppose that the two types of rocks were not contemporaneous is still more unsatisfactory, and is not in accordance with the relations which the beds in both regions bear to the Carboniferous rocks on which they repose. These relations are precisely similar. In some places there is (as it were by accident) conformity, in others, great discordance. To suppose that there are two types of Roth-todt-liegende representing two successive stages of this earliest period of the Permian group, is not in accordance with observation in other districts. On the contrary, the beds of the Salopian type must, I think, be regarded as representatives in time of the Lower Red Sandstone of Lancashire, and both as representatives of the Lower Permian stage, or Roth-todt-liegende of Germany.

careous submarine mud -flats that lay off the coast of a Permian land-area ; the Yorkshire fauna certainly existed further away in deeper water, and within the limits of regular deposition of calcareous sediment."