STATE GEOLOGIST. 53 



The Trenton Oromp of roeki forma ■ belt about four miles 

 wide, extending west-northwest across Si Joseph's Island, re* 



appearing in the high bluffs opposite Little Sailor Encamp* 

 ment Island, and extending thence across the middle of Great 

 Sailor Encampment Island. From here it Btretches weal in a 

 gradually widening belt, which, bending round to tin- south- 

 lies with its Bonthern border on the west shore of Little 

 Lay de Noqoet and Green Bay, whence it continues across 

 Wisconsin into northern Illinois. 



4. — Hudson River Group. 



On the north side of Drummond's Island are found some 

 highly argillaceous limestones abounding- in the fossils charac- 

 teristic of the Hudson Liver Group of New York. These are 

 first Been about three miles west of Pirate Harbor, and extend 

 thence around the coast to the point of land north of the bay 

 which indents the north-west side of the island, thus occupying 

 a belt about three miles wide. A large proportion of the fos- 

 sils seen are Bryozoa, which have not yet been studied. Che- 

 testes lycoperdon is exceedingly abundant. Famstdla vUllata 

 occurs in prodigious masses and great numbers, (at 781, 786, 

 788.) At 781 (A) is an Ambonychia not yet identified. The ar- 

 gillaeeous strata are about lifteen feet thick, and underlain by 

 a bluish gray, s-uberystalline limestone, of which three feet 

 were observed* 



This group forms a belt about four miles wide across St. 

 Joseph's Island, a little south of the middle, then, intercepting 

 southern extremity of Great Sailor Encampment Island, 

 ward al 90Uth side of the region covered 



by the Trenton Group, and occupies the space betwe< d Big and 

 Little Lay- de Noquet Passu g under the whole length of I 

 Lay, it reappears at the southern extremity, and continues in 

 the d ! Winnebago and lb ricon Lakes, in Wisconsin. 



All round the circuit which is thus traced, the dip of the 



itioo carries it under the lower peninsula of Michigan. It 



M the southern side of the peninsula, being 



oveilain by the four groups next described, but dips down 



