500 Geological Society. 
which a permanent alteration in the inhabiting medium may work 
in the form and size of a shell or coral. 
- Of the importance of organic remains in identifying districts less 
widely separated, the two following instances were noticed. In 
M. Dumont’s work on the geology of the province of Liege, pub- 
lished in 1832, and justly valued for unravelling the structure of a 
most intricate country, the strata immediately beneath the mountain 
limestone are divided into three systems, but without any definite 
comparison with the formations which underlie that deposit in 
England. At the meeting of the Geological Society of France, at 
Mezieres, in September, 1835, Dr. Buckland proposed the following 
first comparison between the systems of M. Dumont and the sub- 
divisions of the Silurian system established by Mr. Murchison :— 
Systeme calcareux supérieur. ... .. Mountain limestone. 
(Old red sandstone wanting. ) 
Syst. quartzo-schisteux supérieur. . The Ludlow rocks. 
Syst. calcareux inférieur........The Dudley and Plymouth lime- 
stone. 
Syst. quartzo-schisteux inférieur..The Caradoc sandstone. 
(Builth and Llandeilo flags wanting.) 
Terrain Ardoisier. 
This comparison was principally founded on the resemblance 
of the corals with those obtained at Dudley and Wenlock. M. 
Constant Prevost pointed out the resemblance of the calcaire bleu 
of the systéme calcareur inférieur of M. Dumont with the Plymouth 
limestone, and of the marble of Heer, subordinate to the systéme 
quartzo-schisteux supérieur, with the limestones of Babacombe. 
Mr. Greenough, however, doubted the identity of the Plymouth 
and Dudley limestones, and he stated that he had remarked the 
total absence of the Dudley Trilobites in the systéme calcareux 
inférieur. During the Mezieres meeting, Dr. Buckland identified 
certain beds beneath the mountain limestone near Namur, Di- 
nant, and Huy, and at Engis, with the old red sandstone*; and 
at an ordinary meeting of the Geological Society of France, in 
December, 1837, M. Rozet repeated his belief, that the old red 
sandstone is well developed between Dinant and Namur; and M. 
Constant Prevost stated, that he had also during the Mezieres 
meeting, determined its existence in those districts. In i888, 
M. Dumont visited England for the purpose of examining the 
Silurian region; and on his return to Belgium, he laid before 
the Royal Academy of Bruxelles a table, differing from that of 
Dr. Buckland only in drawing more. closely the terms of com- 
parison, and in identifying the two upper divisions of the Terrain 
Ardoisier with the Cambrian system. He stated also, in a report 
which accompanied the table, that the old red sandstone was 
most probably wanting in Belgium, or, if it exist, that it must 
* In the ‘‘ Outlines of England and Wales” (1822), the Rev. W. D. Cony- 
beare places all the Belgian beds between the carboniferous limestone and 
the transition slates in the old red sandstone.—Note, 468. 
