MICHIGAN ACADEMY OF SCIENCE. 49 



Detroit. Down under 189 feet of Silurian dolomite there is a deposit of 

 limestone 38 feet in thickness, carrying what have hitherto been recog- 

 nized as chiefly Devonian fossil forms and not belonging to the Silurian 

 age. These have been identified by Grabau as very similar to those of 

 the Anderdon beds of high-grade limestone (99% Ca CO3) to which, 

 as a fannal zone of distinctive character, he has given the name "zone 

 of Tdiostroma nattressi." 



Sherzer and Grabau have therefore concluded that this 38 feet of lime- 

 stone in the shaft is the Amherstburg beds intercalated. 



It may therefore be of interest to locate the rocks above the Sylvauia 

 in relation to it as a permanent base, and in relation one to the other, 

 — at various points around the shore of the Detroit river reach of the 

 Cincinnati anticline. As we shall be able to follow this old shore-line 

 from drill core to rock well, shaft and test hole, the area is approxi- 

 mately of horse-shoe outline. The left heel of the shoe will mark the 

 Sylvania in the extreme south-east corner of Wayne county. If there 

 be four nail-holes on each side of the shoe, the first one from the left 

 heel will mark Horse Island and sandrock. The second one will mark 

 the Sibley quarry at Trenton. The third marks the Wyandotte well, the 

 log of which is given in Vol. V., Geological Survey of Michigan, Plate 

 LXVI. The fourth hole locates the Salt Shaft af South Detroit. Let 

 W^indsor Salt Well Xo. 11, (See State Board of Geological Survey of 

 Michigan report, 1901, p. 218,) be indicated by the toe-calk of the shoe; 

 then the second nail-hole on the right will just about mark the Sucker 

 Creek test hole. The third one marks the Amherstburg quarries in 

 Anderdon. The fourth marks the Caldwell Grove well. And the right 

 heel of the shoe will mark the Dr. Green Shaft to the Svlvania at Elliots 

 Point. 



Here is the comparative statement : 



At Sibleys there is a Corniferous (Dundee) deposit over a heavy 

 stratum of magnesian limestone, immediately under which (as shown by 

 drill cores) is a Stromatopora l"reef" associated with what Grabau has 

 described as ''calcilutite," a compact brittle limestone, precisely as in 

 the ''Anderdon beds'' in the Amherstburg quarries, in Essex county. 



In the Wyandotte well there is 50 feet of ''Dundee," (no subdivision 

 reported in the well record) and 105 feet of dolomite, above BO feet 

 of Sylvania. Presumably the Anderdon beds — the coral stromatopora 

 "reef" and the compact calcilutite (Grabau) are present; for the dis- 

 tance from Sibleys is very short, and the depth recorded as Dundee is 

 suflicient, and was so named before the "Anderdon" beds were discovered, 

 — by comparison with both the Amherstburg and Sibley quarries. 



At the Salt Shaft is 63 feet of Dundee (again sufficient depth for the 

 Anderdon beds to be present, other things being equal;) and 189 feet of 

 "Lucas" dolomite next under this depth of Dundee, (Evidently we are 

 getting off shore further from the Cincinnati uplift.) Next below is 38 

 feet of limestone which Sherzer and Grabau together claim is the 

 "Anderdon" limestone, intercalated. That is the problem. 



Under the problematical 38 feet is 47 feet of Flat Rock dolomite, 

 resting upon 117 feet of Sylvania ; the increased depth again suggesting 

 greater distance ofl' shore from the Cincinnati anticlinal than at Wyan- 

 dotte, a heavier deposit in a deeper sea. 

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