732 Mr. Lonsdale on the Age of the 



systhme calcareux inferieur reminded him strongly of the limestones of Ply- 

 mouth, and that the marble of Heer, near Mezieres, composed for a great part 

 of indistinct corals, and subordinate to the quartzo-schisteux superieur, ap- 

 peared to him analogous to the limestones of Babbacombe. (Bulletin, pp. 353, 

 349.) Mr. Greenough expressed doubts of the identity of the Plymouth and 

 Dudley limestones ; and stated that he had remarked the constant absence in 

 the si/st^me calcareux inferieur of the Trilobites, and particularly the Caly- 

 mene Blumenhachii, so common at Dudley. (Bulletin, p. 353.) The above 

 remarks are valuable, bearing upon the question under examination, and they 

 teach us the value of not rejecting from our consideration negative evidence, 

 when attempts are made to compare systems of formations. 



At an ordinary meeting of the Geological Society of France, in December 

 1837, M. Rozet repeated his opinion that the old red sandstone is not want- 

 ing in Belgium, being well developed between Dinant and Namur ; and 

 M. Constant Prevost observed, that during the Reunion of the French Society 

 at Mezieres, he had observed a great mass of psammites, red grits, and 

 quartzose conglomerates in the district mentioned by M. Rozet, actually in- 

 terposed between the Silurian schists and the carboniferous limestones, and 

 representing consequently the old red .sandstone of the English*. (Bulletin 

 Soc. Geol. de France, tome ix. p. 84.) 



In 1838, M. Dumont visited England for the purpose of examining the Si- 

 lurian region, and on his return to Belgium he laid before the Royal Aca- 

 demy of Brussels a comparative tablet of the Belgian and Silurian formations. 

 This document differs from Dr. Buckland's table only in drawing more closely 

 the terms of comparison — in identifying the two upper divisions of the terrain 

 ardoisier with the Cambrian system — and in omitting all reference to the Ply- 

 mouth limestone. The old red sandstone of England is considered to have no 

 equivalent in Belgium. In the Report which accompanies this table, M. Du- 

 mont remarks on the perfect accordance in the structure of the two regions, 

 but he says that in Belgium the calcaire inferieur is most strongly developed, 

 and in Siluria the schists and psammites. He doubts if there be any represen- 

 tative of the old red sandstone in Belgium. If it be wanting, he says, its 

 place is marked between the systhne quarlzo-schisteux supe'rieur and the 

 systeme calcareux supe'rieur; but if it exii-ts, it ought to be regarded as 

 an extraordinary development of the superior psammite of the quartzo-schisteux 

 superieur or upper Ludlow rock. The fossils considered as characteristic of 



* Dr. Buckland has kindly permitted me to refer to some maniuscript sections made during 

 the Mezieres Meeting ; and in those between Namur and Dinant, as v^ell as those near Huy and 

 at Engis, the old red sandstone is exhibited underlying the mountain-limestone. 



t Bulletin Acad. Roy. de Bruxelles, 1838, No. x. p. 634, et seq. 



