44, REMARKS ON THE FAUNA OF THE 
fossilferous rocks of the Mississippi valley, while independent of the 
six species identical with Chazy and Calciferous forms, there are many 
others closely allied to those found in the latter formation in Canada. 
From the physical structure alone, no person would suspect the 
break that must exist in the neighbourhood of Quebec, and without 
the evidence of the fossils, every one would be authorized to deny it. 
If there had been only one or two species of an ancient type, your 
own doctrine of colonies might have explained the matter, but this I 
presume would scarcely be applicable to so many identities in a fauna 
of such an aspect. Since there must be a break, it will not be very 
difficult to point out its course and its character. The whole Quebec 
group, from the base of the magnesian conglomerates and their 
accompanying magnesian shales to the summit of the Sillery sand- 
stones, must have a thickness of perhaps some 5000 or 7000 feet. 
It appears to be a great development of strata about the horizon of 
the Chazy and Calciferous, and it is brought to the surface by an over- 
turn anticlinal fold with a crack and a great dislocation running along 
the summit, by which the Quebec group is brought to overlap the 
Hudson River formation. Sometimes it may overlie the overturned 
Utica formation ; and in Vermont, points of the overturned Trenton 
appear occasionally to emerge from beneath the overlap. 
A series of such dislocations traverses eastern North America from 
Alabama to Canada. They have been described by Messieurs Rogers 
and by Mr. Safford. The one in question comes upon the boundary 
of the Province not over a couple of miles from Lake Champlain. 
From this it proceeds in a gently curving line to Quebec, keeping 
just north of the fortress ; thence it coasts the north side of the 
Island of Orleans, leaving a narrow margin on the island for the 
Hudson River or Utica formation. From near the east end of the 
island it keeps under the waters of the St. Lawrence to within 
eighty miles of the extremity of Gaspé. Here again it leaves a 
strip of the Hudson River or Utica formation on the coast. 
To the south-east of this line the Quebec group is arranged in 
long narrow parallel synclinal forms with many overturn dips. 
These synclinal forms are separated from one another on the main an- 
ticlinals by dark grey and even black shales and limestones. These 
have heretofore been taken by me for shales and limestones of the 
Hudson River formation, which they strongly resemble, but as they 
separate the synclinals of the Quebec group, they must now be consid- 
