ETHERIDGE DEVONIAN ROCKS AND FOSSILS. 695 



these red grits and sandstones. I consider the Devonian deposits as a 

 whole to be equivalent in time with, or chronologically the same as, the 

 Old Eed Sandstone as a whole — and that as it is convenient to divide 

 the series composing the mass of the latter into Lower, Middle, and 

 Upper Old Red by stratigraphical sequence and the fossil fishes which 

 characterize the groupings, so it is also equally convenient and 

 natural to make a threefold division of the marine Devonian Rocks as 

 characterized by the assemblage of organic remains in, and by the 

 physical characters of, each, and especially so through the middle 

 or intermediate group and its great limestone coral-bearing series, 

 this holding good for Europe as well as Britain. 



I believe we may yet be able to demonstrate that the marine De- 

 vonian series of West Somerset and North Devon was deposited in a 

 different area, a different province of life, from that of the Old Red 

 Sandstone; it is a great marine system totally distinct from the 

 Silurian below, and even from its contemporaneous, or synchronously 

 deposited Old Red Sandstone, and that, through its upper members, 

 when or where developed, it gradually passed into the succeeding 

 Carboniferous group — which is incontestably seen and proved to be 

 the case in the North-Devon area. 



We have yet to learn what were the conditions and what the 

 physical changes that took place at the close of the marine Silurian 

 epoch and the commencement of the Old Red Sandstone proper, by 

 which so complete a change took place that almost every species 

 and vestige of invertebrate life changed or passed away, or is not 

 preserved to us, through the whole of that interval of time which 

 witnessed the deposition of the normal Old Red Sandstone series. 

 I believe we can come to no other conclusion than that in the 

 typical Old-Red area the marine Silurian sea was slowly and 

 gradually changed, or was succeeded by long-continued and slow ele- 

 vations and oscillations of the land, thus converting the old marine 

 area into one of freshwater conditions of great extent. The 

 contour of the area over which the Old Red Sandstone of England 

 and Wales extended would favour and lend considerable weight to 

 this view. The oval basin-shaped region or tract occupied by this 

 formation extended from Much-Wenlock on the north to Haverford 

 West and Milford Haven in South Wales, along the junction of the 

 Silurian and Old Red strata at its western boundary, and thence in 

 an easterly direction or strike to Pembroke, Caldy, Worms-Head and 

 across the Channel to the Mendip Hills, and thence again deflected 

 north, along the eastern margin of the Bristol Coal-field, where the still 

 older Palaeozoic rocks and Old Red Sandstone, as well as the Carboni- 

 ferous series, all dip west, this condition being continuous along the 

 strike of the Malvern and Abberley Palaeozoic series and onwards to 

 Bridgenorth. This extensive area, the only one in England occupied 

 by the true normal Old Red Sandstone, though not so extensive as 

 that originally occupied by the Wealden when produced across the 

 English Channel into the Boulonnais, may have been, and indeed very 

 probably was, dui'ing a long interval of time, subject to freshwater 

 conditions, either estuarine or lacustrine, with slow but continuous 



