1889.1 
359 
[Marcou, 
Rosenbuch of Heidelberg, to Messrs. T. H. Bonney, J. J. H. Teall 
of London, or to M. Michel Levy of Paris, all excellent lithologists 
who are trusted by everybody. I hope Mr. Selwyn will not con- 
tent himself with saying that “ it seems almost idle to attempt a.ny 
discussion or explanation about the geology of Quebec with Mr. 
Marcou, because when he has the boldness to assert that the Fall of 
the Montmorency is not over gneiss, in spite of the dictum of ev- 
ery other geologist who has visited and examined it and when . 
The value of the section of the Fall of the Montmorency, made 
by Prof. Capellini is far greater than the three sections published 
by Logan and Mr. Selwyn ; and I do not hesitate to say that my 
own knowledge of the Fall is supported by a “ basis of fact” well 
observed ; while, on the contrary, the sections of Logan and Mr. 
Selwyn with their folded “ Laurentian gneiss” are fanciful to the 
last degree and contrary to what exists there and, according to my 
observations, “ certainly have ‘ no basis of fact’ to support them.” 
The use of the adjective “ Laurentian” with gneiss has not the 
power to change a quartzite into a gneiss. 
Second question : “ What are the sandstones of the Strait of 
Belle Isle if not Potsdam? ” 
Reply: The sandstones designated by Logan, Billings and Rich- 
ardson as A, B, C of their section of the rocks of the Strait of 
Belle Isle “ have nineteen species of fossils, none of which are 
found in the Potsdam sandstone of Canada. In that part of the 
group which is usually known in the State of Vermont under the 
designation of the Georgia slates” (Palaeozoic fossils by Billings, 
Vol. i, p. 371), the following fossils occur: Obolella (Kutorgina) 
cingulata , Olenellus Thompsoni , 0. Vermontana and Conocepha- 
lites Teucer , all most characteristic species of the Georgia forma- 
tion of the upper part of the Middle Taconic, which is far below 
the Potsdam. I do not go so far as Mr. Walcott who, in his last 
paper (“ Stratigraphic position of the Olenellus fauna in North 
America and in Europe,” Amer. J. /Sc., 18891, places the Georgia 
formation, which has the fossil Olenellus Thompsoni , in the Lower 
Taconic. He puts it below the shales with Paradoxides of St. 
John, New Brunswick, and those of St. Mary’s bay, Newfoundland, 
and those of Braintree, Mass. He places the Georgia group in 
parallelism and regards it as the equivalent of the lower part of 
Manuel’s brook section with Holmia (called by mistake Paradoxides 
and Olenellus) Broggeri Walcott. In Mr. Walcott’s judgment the 
i 
