74 KEPORT OP THE 



feet higher than the shales of Thunder Bay and Kettle Point. 

 The Huron county shales and flagstones, however, are the next 

 rocks observed in ascending order. Not less than 180 feet of 

 them, are seen in Huron county, and the total thickness must 

 be much greater. They were penetrated 59 feet in Butter- 

 worth's. salt well at Grand Rapids, 130 feet in the State salt 

 well, and 214 feet in Lyon's well. 



The greater part of this member of the group consists of 

 shales, which are laminated, fissile, dark blue or^blackish, bitu- 

 minous and pyritiferous. Their exposed surfaces generally 

 become covered with rust, and when protected from the 

 weather, with an astringent eflorescence resembling sulphate of 

 iron. Throughout the whole thickness, we find occasional bands 

 of hard limestone and bluish, fine-grained, somewhat argilla- 

 ceous sandstone, which at many points has been manufactured 

 into whet-stones, and might be used for flagging. The more 

 shaly portion is surmounted by a more important mass of the 

 sandstone fifteen feet in thickness, from which the celebrated 

 Huron grindstones are manufactured. The rock here is bluish- 

 gray, fine-grained, perfectly homogeneous, with sharp grit and 

 a limited amount of argillaceous matter. Between the layers 

 are found some serpentine grooves and casts like worm tracks. 

 One of these was traceable twenty-eight inches and was three- 

 eighths of an inch in width. In one fragment the pectoral fin 

 of a fish is preserved. Numerous obscure traces of terrestrial 

 vegetation are found between the strata, and in one place the 

 workmen opened a cavity from which they took out a bushel of 

 good bituminous coal— a discovery which was immedately fol- 

 lowed by a fever! 



The junction between the gritstones and underlying shales, 

 is finely seen at the old quarry, about one mile east of the 

 principal one, the upper fourteen feet being sandstone, and the 

 the lower six, shale. It is again seen at the mouth of Willow 

 Creek, where, near the saw mill, the shale rises six feet, and is 

 overlain by the gritstone. The latter is struck in all the wells 

 of the neighborhood, and forms a high ridge to the east of the 



