Marcou.] 
360 
[Nov. 6, 
Olenellus Thompsoni sandstone of Lance au Loup, Strait of Belle 
Isle, are so far below tlie Potsdam that he places them at the base 
of the Laconic, while the Potsdam sandstone is placed at the top. 
The thickness of strata between them is at least twenty thousand 
feet. But I think this is another great mistake of the adversaries 
of the Laconic who cannot agree among themselves as to the exact 
position of a single group of the system named by them Cambrian. 
A Cambrian of their own making, as far as possible of the original 
Cambrian system of Sedgwick. 
It, therefore seems, that, according to Billings and Mr. Walcott, 
the sandstones of the Strait of Belle Isle are not Potsdam, but be- 
long to the Georgia formation. 
Third question: “ If the Pointe Levis beds are older than the 
Potsdam, why have they never yet been discovered underlying the 
latter? ” 
Reply : Because in the part of the province of Quebec where the 
Pointe Levis beds exist, the Potsdam was not deposited. 
Fourth question: “ Page 69 (op. cit .), we are told ‘we have 
there [vicinity of Quebec], two distinct formations, one of very 
small extent [? thickness] belonging probably to the Trenton and 
another extremely thick, forming the hill of the City of Quebec, 
Pointe Levis and La Chaudiere Falls [here are three very distinct 
series lumped together, Selwyn], strongly upheaved and broken 
before the deposit of the Trenton limestone.’ Why, if this impres- 
sion is correct, is the Trenton limestone, nowhere in its entire 
course of hundreds of miles, seen resting on anything resembling 
this supposed older formation?” 
Reply : “Very small extent” for the Trenton means thickness as 
well as ground covered by the formation. “The hill of the city of 
Quebec, Pointe Levis and La Chaudiere Falls” are mentioned as 
geographical places only ; and instead of having committed the 
mistake of “three very distinct series lumped together,” as Mr. 
Selwyn accuses me ; on the contrary, as far back as 1862, many 
years before Mr. Selwyn came to Canada, I had divided trie series of 
strata into three distinct formations, called then by me Quebec 
group (City of Quebec and not the Quebec group of Logan for the 
whole province), Pointe Levis group and Chaudiere and Sillery 
group (see letter to M. Joachim Barrande , on the Taconic rocks of 
Vermo7it and Canada , p. 9 and following, Cambridge, 1862). The 
statement that I have embraced in one formation “three very dis- 
