STATE GEOLOGIST. 53 



The Trenton Grcm of rocks forms a belt about four miles 

 wido, extending west-northwest across St. 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 stretches west in a 

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

 west, lies with its southern border on the west shore of Little 

 Bay de Noquet and Green Bay, whence it continues across 

 Wisconsin into northern Illinois. 



4. — Hudson Biver Group. 



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

 highly argillaceous limestones abounding in the fossils charac- 

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

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

 thenco 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- 

 tcetes lycoperdon is exceedingly abundant. Famstella stellata 

 occurs in prodigious masses and great numbers, (at t81, 786, 

 788.) At 181 (A) is an Ambonychia not yet identified. The ar- 

 gillaceous strata are about fifteen feet thick, and underlain by 

 a bluish gray, subcrystalline 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 

 the southern extremity of Great Sailor Encampment Island, 

 stretches westward along the south side of the region covered 

 by the Trenton Group, and occupies the space between Big and 

 Little Bays de Noquet. Passing under the whole length of Green 

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

 the direction of Winnebago and Iloricon lakes, in Wisconsin. 



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

 formation carries it under the lower peninsula of MicLigan. It 

 does not emerge on the southern side of the peninsula, being 

 overlain by the four groups next described, but dips down 



