MICHIGAN ACADEMY OF SCIENCE. 
113 
requirements of channel deepening. These also, on Ihe same evidence 
and according to my own observation, are different strata from any 
south of them within the compass of our investigation. 
Now, since the characteristic folding at the surface of Ihe Silurian 
took place at the close of the Silurian age, and not during its continu- 
ance, it follows that the depth of strata laid down would be approxi- 
mately proportionate to the distance in the direction from which newer 
strata were added on. Our distance from south to north is: 8,500 ft. 
-f- 5,700 ft. -j- 9,000 ft. ■ 23,200 ft. In the 5,700 ft. reach, as stated, 
about 105 ft. in depth of strata was exhibited in the dry cut. That 
gives approximately 10 425 ft. of strata to be accounted for, all dolomite, 
and no trace of either Anderdon limestone beds or further trace of 
Sylvania sand within that depth and distance. The Corniferous strata 
and associated Anderdon limestone beds must, therefore, cross the De- 
troit river between the upper end of Grosse Isle and a point about 
abreast of the Salt Shaft at Delray, where the Corniferous (Dundee) is 
a surface extension. 
Commenting upon the Devonian aspect of the Anderdon and Salt 
Shaft faunas, one gentleman of recognized position and ability has 
remarked, “With me, the most serious part of the proposition is that 
the fossiliferous horizon in the bed of the Detroit river carries a fauna 
also remarkably Devonian in its affinities.” Whiteaves was of the same 
opinion at the time of his naming the Panenka Canadensis. Hence the 
confusion that has arisen. 
Collections have been made from the fossil contents of these river-bed 
strata by the State Geological Department at Lansing, by the Dominion 
Survey at Ottawa, by Yale University, and by the University of Toronto, 
in addition to private collections. Consequently there is no lack of 
data for comparison. Stratigraphy and palaeontology seem to be in 
conflict. But, should the river-bed horizon, in relation to the Sylvania 
and to the Anderdon, still be held to be in dispute there is but one 
thing to do, and that is to take out a core at Stony Island in Detroit 
river and let it become the standard of reference for this area. 
THOMAS NATTRESS. 
Ainherstburg, Ontario, February 19, 1912. 
1 °To this approximation of 425 ft. must be added the 248 ft., or thereabout, of dolomitic limestone 
and dolomites between the bottom of the Anderdon and the top of the Sylvania in the Colwell Grove 
well to get the total depth of dolomite exposed in the Detroit Diver bed and in its immediate neighbor- 
hood on the Essex County side. That total thus obtained is 673 feet. 
