Age of the Limestone of South Devon. 223 



of the previously noticed cases, and the texture bore a greater affi- 

 nity to that of the freshwater sponge, than is exhibited in the flints 

 of the chalk or the cherts of the green sand. 



With respect to the causes of the deposition of the flint, Mr. Bower- 

 bank objects to the supposition, that it was influenced by the silice- 

 ous spicula of the sponges, because the flint is in no case limited or 

 determined by their immediate presence, but is, in all instances, bound- 

 ed by the extent of the animal matter of the sponge. He has fre- 

 quently observed that the large excurrent canals in the chalk-flint 

 spongites are not filled with silex, and that the spicula projecting into 

 them have not the slightest incrustation of siliceous matter upon 

 their surface ; while on the contrary, M'herever a single tube or 

 a thin layer of tubes has been projected from the mass into the 

 chalk, the silex has been attracted to it. He conceives also, that the 

 retention of the spicula and extraneous matters in all parts of tiie 

 flint, may be accounted for, by supposing that the animal matter was 

 the attractive agent, acting equally throughout the whole body of 

 the sponge. In support of his argument he adduces the siliceous 

 shells of Blackdown, and the siliceous corals of the Tisbury oolite 

 and the mountain limestone, which contain no spicula, and in M'hich 

 it cannot be supposed that pre\dously existing siliceous matter was 

 the attractive agent. Lastly, the pyritous fossils of the London, 

 Kimmeridge, Oxford and other clays, are also mentioned as exam- 

 ples of animal and vegetable substances having exercised an attract- 

 ive influence. 



March 25, 1840. — A paper was first read " On the Age of the 

 Limestones of South Devon ;" by W. Lonsdale, F.G.S. 



The object of this communication is to show the nature and limits 

 of the author's claim to having been the first to infer from zoological 

 evidence that tiie limestones of South Devon would prove to be of the 

 age of the old red sandstone; and it was drawn up at the request of 

 Mr. Murchison, in consequence of the subsequent adoption and ex- 

 tension of the proposed classification by Professor Sedgwick and 

 that gentleman ; and at the request likewise of Dr. Fitton, in conse- 

 quence of the same views having been applied to some of the in- 

 fra-carboniferous formations of Belgium and the Boulonnais. The 

 paper commences with a summary of the opinions previously enter- 

 tained respecting the age of the limestones. The authors quoted are, 

 Woodward, 1 722 ; Da Costa, Maton, Play fair, Berger, L. A. Necker, 

 De Luc, T. Thomson, Kidd, W. Smith, Brande, W. Phillips, Hennah, 

 Greenougli, Sedgwick, W. Conybeare, J. J. Conybeare, Buckland, 

 Dufrenoy, Elie de Beaumont, De la Beche, Pritleaux, Boase, J, 

 Phillips, Austen, Murchison, Bakewell and J. de Carle Sowerby. 



By these geologists the limestones are placed in the ])rimary, trans- 

 ition or gray wacke and carboniferous series ; Mr. Prideaux being 

 the only author who ascribes them in part, and on mineral characters, 

 to the old red sandstone ; and Mr. J. Phillips, in his article on geo- 

 logy in the Encyclopedia Mctropolitana, hesitating to place them 

 in a definite position, in consequence of the resemblance of many of 



