Limestones of South Devon. 735 



cient formations of the Bas Boulonnais, which he had visited during- the pre- 

 ceding summer, in company with MM. d'Omahus d'Halloy and Dumont, 

 previously to a joint excursion to England. The principal object of the pa- 

 per was to establish the existence of two limestones, one the equivalent of the 

 mountain-limestone of England, and the other of the Wenlock, M. de Ver- 

 neuil having been led to suppose that there existed in the Bas Boulonnais 

 a true Silurian district, in consequence of the examination of a collection of 

 fossils sent to him, the preceding autumn, by M. d'Archiac. This limestone 

 M. de Verneuil also placed on a parallel with the systbne calcareux in- 

 ferieur, of M. Dumont and of the limestone of the Eifel. (Bulletin Soc. 

 Geol. de France, tome ix. pp. 388, 389 ; 1838.) 



M. Dumont, in the Report made to the Bruxelles Academy in 1838, likewise 

 states, that his four st/stemes anthraxijeres of Belgium are found in tlie Bou- 

 lonnais. (Bulletin Acad. Roy. de Bruxelles, 1838, No x. p. 638.) 



M. Rozet had previously (1828) pointed out the existence of two lime- 

 stones, the upper of which he placed on tiie parallel of the mountain-limestone, 

 and the lower or black beneath the old red sandstone, which he stated was 

 wanting in the Boulonnais; but in his memoir on the Ardennes and Belgium 

 he considers them as two divisions {etages) of the same formation, and assigns 

 them a position above the old red sandstone. (Description Geologique du 

 Bas Boulonnais, pp. 99, 117, 1828; Annales des Sciences Naturelles, tome 

 xix. p. 145, 1830.) 



It is not necessary to offer any remarks on the proofs of the existence of the 

 mountain-limestone, for it has been long known to occur in the Bas Boulonnais. 



The evidence in support of the presence of an ecjuivalent of the Wenlock 

 limestone rests partly on infraposition, and |)artly on certain fossils, stated to 

 be common to the Boulonnais, Dudley, Wenlock, the Eifel, and Belgium. 

 (Bull. Soc. Geol. de France, tome. ix. p. 392.) 



At the Reunion extraordinaire of the French Society at Boulogne in Sep- 

 tember last (1839), and at whicli some of the Fellows of this Society assisted, 

 M. de Verneuil's views with respect to that limestone were fully admitted. 

 When, however, doubts arose at the commencement of this year relative to 

 the age of the Belgian sjjsthnes, Mr. Murchison suggested to me, that the 

 Boulonnais beds would prove to be of the equivalents of the Devonian. It is 

 necessary to state, that Mr. Murchison attended the meeting of the French 

 Society. To determine the question, if possible, by the aid of organic re- 

 mains, that gentleman procured, by the kind assistance of M, Dutertre-Yvart, 

 a collection of specimens in the Boulogne Museum. 1 have had the pleasure 

 of examining it, and comparing its contents with the list drawn up by M. de 

 Archiac and M. de Verneuil, and published in the French Bulletin. 



The following are the results obtained from both sources of information ; 



