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IOWA ACADEMY OF SCIENCES. 
MAQUOKETA SHALES IN DELAWARE COUNTY. 
BY SAMUEE CALVIN. 
(Abstract.) 
Prom the relation of Delaware county to the great Niagara 
escarpment it would scarcely be expected that rocks older than 
the Upper Silurian would be found within its limits. Upper 
Silurian sediments indeed constitute the rocks that may be said 
to be normal to the entire county. They cover probably ninety- 
nine per cent of its area. Without exception all the higher 
lands are occupied by them, and most of the valleys have a floor 
of Niagara dolomite. Still some of the valleys have cut through 
the Niagara limestone down into the underlying shales of the 
Maquoketa age, and very many of the valleys come much nearer to 
exposing Maquoketa shales than has hitherto been supposed. The 
normal dip of the Iowa strata to the southwest is evidently 
reversed along a line that passes obliquely near the northeast 
corner of the county, so that the Maquoketa shales are covered 
with a relatively thin veneer of Upper Silurian dolomite, even 
as far as the western border of the county in the northwestern 
corner. 
Northeast of Colesburg the valleys of some small creeks, trib- 
utary to the Turkey river, have cut through the Niagara, and 
exposed the Maquoketa shales' at an altitude 200 feet lower 
than the ridge on which the village is situated. A section of 
the shale more than 50 feet in thickness is exposed in sections 
1 and 2 of the northeast township of the county. The shales at 
this point are composed of blue, plastic clay. They are non- 
fossiliferous, and are well adapted to the manufacture of pot- 
tery, a use to which they are put on a limited scale by Mr. 
Prank Brock, of Colesburg. 
In section 2 a large spring issues from the side of the hill at 
a level corresponding to the top of the blue shales. Above the 
level of the shales there are 25 feet of rather thin-bedded. 
