34G PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



out the Central Palaeozoic area of Middle North America. This is 

 well and abundantly seen on Lake Cham plain and in the great 

 valleys of the Hudson, Mohawk, Black, and other rivers. It doubt- 

 less underlies, in its place among the fossiliferous strata, the whole 

 of the vast levels in the United States, east of the Mississippi. It is 

 well seen in the great fissures on the Rivers Ohio and Cumberland, 

 and surrounds, in an extensive mass, the Ozark Mountains of 

 Missouri. 



One of its most distinct northern outcrops runs from Fonda or 

 the Mohawk, by Mexico Bay and Cobourg on Lake Ontario, Nota- 

 wasaga Bay, and the Manitoulines Isles in Lake Huron to neai 

 Grand Isle, Lake Superior (south shore), about 750 miles. From 

 this point the outcrop of this slate passes south several hundred 

 miles through an imperfectly-explored country, in its proper geolo- 

 gical position. From Fonda, north-eastwards, it has been traced to 

 Quebec, a distance of 317 miles. 



Position. — Where not disturbed by intrusive rocks, or by post- 

 carboniferous movements, Utica Slate dips slightly to the south-west. 

 The uplift it undergoes at East Canada Creek will be mentioned in 

 another place. 



Thickness. — This varies. It is 250 feet in Montgomery County 

 (Vanuxem), and 7b feet in the gorges of Loraine and Rodman, more 

 to the east in this State (Emmons). 



Fossils. — Utica Slate only yields 48 species of fossils, as we learn 

 from Table I. Its upper part is not fossiliferous, except in Jefferson 

 County, where it is richer than in the lower portions (Emmons). 

 Most of the Trenton fossils perished ; only sixteen Brachiopoda 

 are received here. 



Twenty-two fossils first appear here ; twenty-six have been received 

 and transmitted (Table II.). Perhaps, from containing too much 

 clay, this series of deposits was unfavourable to animal life. 



Fossils typical. — These are strikingly so ; but they are only ten ; 

 some of the principal orders, the Brachiopoda, Zoophyta, Mono- 

 myaria, and Gasteropoda, being unrepresented. 



Fossils occurrent in Europe. — No Crustacea. Didymograpsus sextans ; 

 Diplograpsus mucronatus; D. ramosus; Graptolites Sagittarius; Discina 

 crassa; Leptaena alternata; L. depressa ; L. Stroph. grandis; Lingula 

 curta ; L. quadrata ; Orthis parva ; O. testudinaria ; Spirifer biforatus ; 

 Terebratula bidentata; T. reticularis; Clidophorus planulatus ; Modio- 

 lopsis modiolaris ; Nucula poststriata ; Porcellia ornata ; Bellerophon 

 bilobatus. 



Fossils recurrent in New York. — These are almost altogether 

 confined to the Trenton and Hudson-River groups, with an occasional 

 escape into the Clinton group, and, in two species of Leptcena, the 

 passage, group by group, into the New York Devonian system. 

 See General Table and Table of Recurrency. 



Hudson-River Group. 

 Mineral character. — This group consists of shale and shaly lime- 



