77 
[Marcon. 
two miles east of the village of St. Armand, near the Vermont line. 
It was not deposited in the whole valley of the St. Lawrence beyond 
Chicot creek and Cache river in Berthier county, while near St. 
Cuthbert it is seen to be represented by a white sandstone, as at 
Keeseville, containing marks of Protichnites. There the Trenton 
lies in discordance of stratification against it, showing the existence 
of the break between the Potsdam and the Champlain system. 
There is no trace of Potsdam east of St. Cuthbert, nor in New- 
foundland, Cape Breton, Nova Scotia, etc. In fact, the Potsdam 
is a local group deposited round the Adirondack mountains, and 
its extension westward demands careful researches before being 
accepted. 
BREAKS IN THE PROVINCE OF QUEBEC. 
In the eastern part of the province of Quebec, all was dry land 
and terra jlrma after the great break and overturn of the Taconic 
slates. I do not mean to say, that there were no breaks before ; 
very likely several breaks, more or less important, occurred during 
the deposition of the Taconic rocks, but further researches are nec- 
essary to determine their position and make a proper classification 
of the breaks and upheaval, some of which, as at Quincy and 
Braintree, near Boston, at St. John, New Brnnswick and at Ste 
Mary’s bay, Newfoundland, are already known. 
After the deposition of the Potsdam sandstone a break — on a 
much smaller scale than the great Taconic break — occurred on the 
coast line with a crack entering the dry land at the contact line 
of the Primitive rocks of the Laurentine mountains with the Ta- 
conic slates ; a part of the land subsided on that crack and the 
Champlain sea extended a narrow arm or gulf, like the Adriatic 
sea or the Red sea, along the actual valley of the St. Lawrence, as 
far as Western Newfoundland. At the end of the deposition of the 
Champlain system rocks, another break occurred, the result of 
which was an upheaval movement of all that narrow gulf, where 
lay the Champlain strata ; while at the same time a corresponding- 
depression and subsidence, local and very limited, brought the Si- 
lurian sea into a very small part of the Taconic land area from 
Gaspe to Lake Memphremagog. This part of the Silurian sea did 
not communicate — at least directly — with the sea of the state of 
New York and the province of Ontario, where typical deposits of 
the Silurian system exist. The Silurian strata of Quebec possess 
all the characters of a littoral formation deposited in a narrow gulf, 
