THE CAMBHIAN. 27 



In Western Europe, as Hicks has shown, great movements of 

 depression must have occurred in this period, and we have evidence 

 of a similar character in America. If we roughly divide the Cambrian 

 system into three great series, characterized respectively by the pre- 

 valence of the large Trilobites of the genera Olenellus, Parudoxides, 

 and Dikdlocephalus, we shall find that the former, the true Lower 

 Cambrian, extends somewhat widely over the great continental 

 plateau of America, being found in the St Lawrence valley, in 

 Vermont, and even in Nevada and Utah,* and the Rocky Moun- 

 tains of Canada. The second or Paradoxides group is more 

 properly a marginal deposit formed at a time when there was 

 probably a great continent west of the then infant Appalachians. On 

 the other hand, the upper members of the Cambrian, tlie Dlkello- 

 cephalus-grouTp or Potsdam Sandstone, is apparently altogether absent 

 in the Acadian provinces, which at that time must have been under 

 ocean-depths in which deposits of a very different kind would be 

 produced, or elevated into laud, perhaps the border of an Atlantic 

 island now mostly submerged. It seems doubtful if any good equiva- 

 lent of the Potsdam exists in England or Wales. 



It is otherwise, however, with the next succeeding formation, that 

 passage-series between the Cambrian and Ordovician known in Wales 

 as the Tremadoc. This, in America, takes a more inland position, 

 and becomes an interior or submarglnal formation connected with 

 the Quebec group. It has not yet been recognised in Acadia, but 

 at Matane and Cape Rosier, as noted by me in 1883, f and as Lap- 

 worth has more fully proved in 1886, J we have a true Tremadoc 

 filled with Dicfyonema sociale, and containing also fragments of 

 characteristic Trilobites. Further inland, on the main American 

 plateau, these beds are not found, but are represented by the peculiar 

 " Calclferous " fonnation, a dolomite formed apparently in an inland 

 sea and having a characteristic fauna of its own. 



Before leaving the Cambrian, it may be well to state that Mr 

 Matthew informs me that he hopes to make out in the St John scries 

 the equivalents of all the subdivisions of the Paradoxides zone estab- 

 lished by Linnarson in Sweden, so tliat there would seem to be a 

 correspondence even In the minor details of the deposits on the 

 opposite sides of the Atlantic. This, as we shall sec, also appears to 

 Prof, Lapworth to hold In the case of the Graptolltic fauna of the 

 Upper Cambrian and Ordovician on the two Atlantic margins. 



* Walcott, Bulli'tins, U.S. Gcol. Survey; M'Coiiiiell, Ueport of 1886. 



t Keport J'etcr Ivedpatli Museum, No. ii., Kicliardson's Observations at MatiUic. 



t Transactions Royal Society of Canada. 



