CHAPTER VIII 



DEVONIAN AND OLD RED SANDSTONE SYSTEM 



GENERAL CLASSIFICATION AND SUBDIVISIONS 



WE have seen in the last chapter that, where complete sections are 

 found, the Silurian rocks pass upwards into a thick series of red 

 sandstones (England and Scotland), or into an equally thick series 

 of grey and purple grits (Ireland). It will be shown in a future 

 chapter that the marine Carboniferous rocks always rest upon a set 

 of red and yellow sandstones, which often repose unconformably 

 upon some of the more ancient Palaeozoic strata. The marine fauna 

 of the Silurian dies out at the base of the red sandstones, and 

 when we reach the next marine fauna that of the Carboniferous 

 System it is totally different from the preceding, so that a long 

 period of time must have elapsed between the close of the Silurian 

 era and the commencement of the Carboniferous. 



The groups known as the Old Red Sandstone in England and 

 Scotland, and the Glengariff grits or Dingle Beds in Ireland, are 

 clearly some of the rocks which were formed in this interval ; and 

 if these were the only records of this portion of geological time, we 

 might find it convenient to regard the whole of the beds whi-h 

 succeed the Silurian Series in conformable sequence as belonging to 

 the Silurian System. 



But these are not the only strata which are interposed bet\\vt-n 

 the Silurian and Carboniferous Systems. In Devonshire, and in 

 many localities in Europe, there is a thick series of rocks contain- 

 ing a marine fauna which is evidently of intermediate age ; further, 

 in Germany the stratigraphical proof of their interposition between 

 Silurian and Carboniferous rocks is complete. It is this marine 

 series which must be taken as the normal type of the intermediate 

 system, and any freshwater deposits which can be shown to be of 

 the same age must be treated as local contemporaneous or homotaxial 

 strata. In America also both types of the Devonian System are 

 present. 



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