58 EEPOET OF THE 



interrupted by the death of one of the proprietors, and has not 

 since been resumed. 



At a higher level, we find at the base of Mackinac, Round 

 and Bois Blanc Islands, as well as at Sitting Rabbit on the 

 main land west, a fine, ash colored argillaceous limestone, con- 

 taining abundant acicular crystals, and becoming in the lower 

 part banded with darker streaks of aluminous matter, and 

 resembling the water limestone of this group in New York. 

 Above this, at the west end of Bois Blanc Island, are found 

 three feet of calcareous clay or marl; while still higher and 

 immediately underlying the rocks of the next group, occurs at 

 all the above localities, a fine-grained, brown limestone. No 

 fossils' have been discovered in this group, in the northern part 

 of the State. 



Prom the region just referred to, this belt of rocks passes 

 under the bed of Lake Huron, reappearing on the Canada shore 

 1 etween the river Au Sauble and Douglass Point. It thence 

 extends to Gait, in Canada West, and crosses the Niagara 

 river south of Grand Island. On the west, it passes in a simi- 

 lar manner under the bed of Lake Afichigan, and barely makes 

 an outcrop in the vicinity of Milwaukee, whence it has not» 

 been certainly distinguished from the associated limestones of 

 the Clinton, Niagara and Helderberg groups, the entire assem- 

 blage being commonly known as the " Cliff Limestone." 



No other outcrop of rocks of this group has heretofore been 

 known in our State. I have now, however, to announce the 

 existence of the Onondaga Salt Group in Monroe county, in the 

 south-eastern corner of Michigan. My attention was first at- 

 tracted by the peculiar character of the limestones at Mont- 

 gomery's quarry, in the south part of the township of Ida. At 

 this place I found the characteristic acicular crystals in great 

 abundance, in a light, thin-bedded, fine-grained, argillaceous 

 limestone; and discovered also, some beds of the brownish 

 banded argillaceous rock forming the water-limestone of the 

 group. At this place occur the only fossils yet detected in the 



