48 TWELFTH REPORT. 



from SoiTthern Michigan," issued in 1907, by Professor W. H. Sherzer 

 of Ypsilanti and Professor A. W. Grabau of New York, conjointly, and 

 bearing the imprimatur of Dr. Alfred C. Lane, then »State Geologist for 

 Michigan. 



The ascertained fact, revealed by the Dr. Green Shaft at Elliot's Point 

 that the Svlvania sandrock, which is a surface extension abreast 



of the south third of Bois BJanc island and across the river bottom of 

 the east channel, has disapi>eared soutlnrard in a distance of a few 

 hundred yards till it lies under about 25 feet of Silurian strata, shows 

 where the sandrock belongs. 



Sherzer and Grabau represent it as dipping under the Stony Island 

 anticline. 



The rock in the channel immediately west of Bois Blanc has all been 

 scraped in dredging, where mud-covered. The drill has been used to a 

 depth of 14 feet where the rock surface rises again, 6,500 feet south- 

 south-wiest from the south third of the island. No sandrock has been 

 touched, as it would have been had it extended across Detroit river. 

 The reason is IT DOES ^^OT BELOXG THERE. 



When Schuchart of the U. S. National Museum at Washington pre- 

 pared his paper '"On the Faunal Provinces of the Middle Devouic of 

 America, etc." and published in The American Geologist in September, 

 1903, he made use of two palaeographic maps, one of Onondaga time, 

 the other of Hamilton time. It is evident to me from study of the 

 Stony island cut and of the Sylvania sandrock exposures and eleva- 

 tions, that he does, not figure either the Cincinnati Peninsula in the 

 one case or the. Cincinnati island in the other, as extending as far north 

 as they did extend. There doubtless has always been more or less of 

 a trough — perhaps a succession of troughs — across the peninsula or 

 island between the head of it as figured by Schuchert and the actual 

 head of it as constituted by the pre-Sylvania anticline knoAvn as Stony 

 island and associated area in Detroit river. 



The proximity of the west and east sides of Detroit river, and the 

 close neighborhood of the corresponding exposures of Sylvania, have 

 hitherto blinded everybody concerned to the fact that these respective 

 exposures are on opposite sides of the Cincinnati anticline. 



The contour of the Sylvania sandrock follows from the Ohio state 

 line, about where it is joined by the county line between Monroe and 

 Adrian counties, diagonally across Monroe and into the extreme south- 

 east corner of Wayne couiity. And then, (as I am persuaded,) follows 

 approximately the* line of the west or Trenton channel of the river till 

 it rounds the head of the northern projection of the Cincinnati anticline 

 about or beyoud the head of Gross Isle; thence circling into and through 

 Sandwich and Anderdon townships in the county of Essex, Outario, it has 

 its first exposure .as a surface extension in Canada — and probably the only 

 one — in the bed of Detroit river and on Bois Blanc island, at the south- 

 ern limit of Amherstburg. Thence it strikes south-easticard and is found 

 under some 222 feet of ''fossiliferous limestone'' on Pelee Island; and 

 might be expected to show in rock wells along a line from Sandusky 

 Bay to Adams county, Ohio, and approaching— if not crossing — the 

 Kentucky state line. 



There is an associated problem presented in the Salt Shaft at South 



