104 B.EPOET — 1872. 



Below all these come the well-marked Lower Silurians^ the equivalouts of the 

 British Oaradoc and Llandeilo formatious. 



Between the Middle and Upper Silurians of the United States there is scarcelj' a 

 single species in common. Representative species occur ; and wheneTcr the phy- 

 sical conditions have been similar during the two epochs, the species occurring in 

 those beds bear a close similarity to each other. 



The author alluded to the opinion of JMr. Warshen, that the Lower Ilelderberg 

 gToup should be placed with the Niagara group, and expressed his strong dissent 

 from those views. lie traced these rocks for several hundred miles in their 

 westerly range from the Schoharie valley, and said that in that direction the 

 Lower Ilelderberg group dies out, whilst the Water-lime and the Onondaga Salt 

 group considerably expands. To the east and south of the Schoharie valley the 

 Lower Ilelderberg group always occurs, and is everywhere underlain by the AVater- 

 lime formation. In Canada the Lower Ilelderberg gi-oup is largely developed, 

 whilst the Niagara group scarcely exists there. 



The author contended that throughout all this vast area the physical fact of 

 superposition and the evidence of fossils coincide to prove the Lower Helderberg 

 group a distinct and overlying formation to the Niagara group, and separated from 

 it by the Onondaga Salt group and Water-lime formatious, wherever these latter 

 formations exist. 



It appears, however, that in parts of Tennessee the Lower Helderberg and 

 Niagara groups do sometimes come into contact from the local thinning-out of the 

 intermediate groups. But upon this Prof Hall remarked that while the actual 

 phj'sical and zoological distinction can be traced in a westerly direction for more 

 than twelve hundred miles, in a north-easterly direction for six or eight hundred 

 miles, and for an equal distance in a southerly and south-westerly direction, lie 

 could scarcely suppose that the few facts observed within limited areas, and not 

 yet submitted to the test of comparison, would change the views of geologists upon 

 the distinctive character of these formations. 



On the Chalk of the Paris Basin. 

 By M. HUBERT, Professor of Qeology in the Sorbonne, Paris. 



This communication was made by M. Iltibert, as the result of his researches on 

 the Chalk of the Paris basin. It was illustrated by two sections, the first of 

 which represents the cliffs of the channel from Havre to Boulogne, the second 

 giving a section from Le Perche, a district which borders Brittany on the east, to 

 Belgium. The characters which, according to M. Plebert's classification, divide 

 the beds are so well mai-ked, that it is possible to ascertain the point where one 

 division ends and another begins. At this point not only does the fauna change 

 abruptlj', but also the lithological differences are equally clear ; besides, the sur- 

 face of one division is always hardened and eroded more or less. There is no 

 passage of the lower-lying hard beds into the soft upper chalk. These lines of 

 separation are always more numerous than the pala'.ontological divisions ; but two 

 paheontological divisions are always unconnected. These characters, in M. Ilebert's 

 opinion, remove all difficulty ; and in submitting the results of his researches to 

 those English geologists who interest themselves in the chalk, he hopes to convince 

 them of the exactitude of the divisions he has proposed; and he would refer them 

 to the cliff's of Kent, ^vhich afford an exact copy of those of the opposite shore 

 of France. 



The divisions which M. Ilebert has established are as follows in ascending order: — 



1. Glauconitic challv, the equivalent of the Upper Greensand and grey chalk. 



2. Chalk with Inoccrcmuis hihiatus, or chalk marl, and chalk without flints, and 

 a portion of the chalk with flints. 



3. Chalk with 3Iicraster cor-tcsti(dinarium, having for its base the zone of Ilolas- 

 tcr j)l(i>tus, and which corresponds to a portion of the chalk with flints. 



4. Chalk with Micraster cor-anguimnn, chalk witli ilints. 



5. Chalk with Bcknmitella inucronaia, Norwich Chalk. 



The Chalk of the Paris basin forms several parallel folds, which correspond 



