542 PROCEEDINGS OF THE ALBUQUERQUE MEETING 



DiSCONFOEMITY : Ppgj p^^j 



Lower Monroe dolomites to salt, as shown by preliminary well 



records '. 334 STI 



AXDERDOX EXPOSL'RE 



The only exposure of tbe intercalated coral limestone is found on the opposite 

 side of the river in the Anderdon quarry, in Anderdon township, Essex county, 

 Ontario, about 2 miles east of Auiherstburg and 15 miles south of Detroit.' It 

 is from this locality that the formation takes its name. In the quarry about 

 30 feet of Dundee is shown, and immediately below it lies the Anderdon, of 

 which about 30 feet are exposed by the quarrying operations. The contact be- 

 tween the Dundee and Anderdon is clearly a disconformable one, as shown not 

 only bj' the absence of the 189-foot Flat Rock dolomite, which in the salt shaft 

 at Detroit intervenes between the Dundee and Anderdon, but also by pro- 

 nounced erosion features on the Anderdon. The top of this bed, where freshly 

 uncovered by the removal of the Dundee, shows sections of large gastropod 

 and cephalopod -shells (Trochonema and Trochoceras), which were partly 

 worn away before the Dundee was deposited on the erosion surface. Further- 

 more, old solution fissures in the upper surface of the Anderdon were filled by 

 the lime sands which form the basal part of the Dundee. 



In one part of the quarry the Anderdon limestone is a great coral and 

 Stromatopora reef, while in other parts it is for the most part a finely bedded, 

 compact calcilutite (consolidated limestone mud) with conchoidal fracture 

 and of great purity. Analyses have shown that it contains over 99 per cent 

 CaCOa, wliile in compactness and texture it suggests lithographic stone. 



SIBLEY COrtE AND OTHER EXPOSURES OP ANDERDON 



About 6% miles northwest from the Anderdon quarry in the drill cores at 

 Sibley the Anderdon was again found to have the coral-reef facies and to 

 underlie directly the Dundee. Between the two on Stony island and on Grosse 

 isle a brown dolomite is shown, to which further attention is invited. Some 

 of the best exposures formerly to be found were in the old Patrick quarry, at 

 the south end of Grosse isle, in the Detroit river. At present the quarries at 

 Gibraltar, 3 miles west of the Patrick quarry, furnish excellent exposures of 

 this rock. Other good exposures are in the Woolmith quarry, near Scofield, 

 15 miles southwest from Gibraltar, and at Sylvania and neighboring regions in 

 northwestern Ohio. In all these cases it lies but a short distance above the 

 Sylvania sandstone, which indeed is sliown beneath it in the Woolmith quarry 

 and at Silica, near Sylvania, Ohio. Two divisions are generally recognizable — 

 a lower magnesian calcarenite, with a fauna transitional between that of the 

 Anderdon and the overlying bed, and the upper a gray dolomitic calcilutite 

 with a gastropod fauna. This upper bed, of which from 30 to 40 feet are 

 shown in the quarries, is the typical Lucas formation of Ohio, so named by 

 Prosser from the outcrops in Lucas county. For convenience it may be de- 

 sirable to designate the lower calcarenite by a special name, that of Amherst- 

 burg dolomite being perhaps the best available one, since this bed forms the 



^ Nattress : Ninth report of the Michigan Academy of Science, p. 177 ; Ontario Bureau 

 of Mines, 1904, part ii, p. 41 ; also report for 1902, p. 123. 



i 



