BIGSBY — PALAEOZOIC ROCKS OF NEW YORK. 343 



a line extending from Champion nearly direct to Watertown. This 

 stratum is in many places altogether wanting, and where it was 

 expected, as at Essex, the village mentioned already. 



Position. — It is conformable with its coterminous strata. 



Thickness. — Very various ; 30 feet on the average, and thinning 

 towards the south. 



Fossils. — See General Table. Some of the Orthocerata are ten feet 

 long by one foot broad (Emmons). 



Fossils typical. — Fucoides demissus ; Phytopsis tubulosa ; P. cellulosa ; 

 Streptelasma profunda ; Strictopora labyrinthica ; Leptaena filitexta ; L . 

 lsevis ; Modiolopsis nuculgeformis ? ; Modiola ? obtusa ; Natica, sp. ind. ; 

 Murchisonia varicosa ; M. ventricosa ; Pleurotomaria nucleolata ; P. nodu- 

 losa ; P. quadricarinata ; P. obsoleta ; Lituites undatus ; Orthoceras fusi- 

 forme ; O. recticameratum ; Cytherina, sp. ind. ; Ellipsolites (Emmons, 

 p. 385) ; Asaphus extans ; Calymene multicosta ; Ogygia ? vetusta. 



Fossils occurrent in Europe. — Ampyx ; Illaenus crassicauda ; Murchi- 

 sonia angulata ; Lituites convolvens. 



Fossils recurrent in New York. — Chaetetes lycoperdon; Stromatocerium 

 rugosum ; Murchisonia angustata ; M. perangulata ; Pleurotomaria umbi- 

 licata ; Illsenus trentonensis, &c. See Table of Recurrency. 



Trenton Limestone. 



Mineral Character. — This limestone is black or dark-blue below, 

 and thin-bedded. Higher up it is thick-bedded, grey, granular, 

 and subcrystalline. From this point, argillaceous shale, which is 

 always more or less interlaminated, increases by degrees, until it 

 forms the whole mass of the rock. 



Transition. — Usually Trenton Limestone graduates from Birdseye 

 by the slow introduction of Trenton fossils (Putnam's Quarry, &c, 

 Vanuxem). It may succeed any of the three preceding groups in 

 shaly layers, or in compact calcareous strata separated by shaly 

 laminae. 



Well-characterized Trenton Limestone rests immediately on Calci- 

 ferous Sandstone at the Falls, near Straker's Basin, and other places. 

 At Fort Plain and elsewhere it lies upon Birdseye Limestone without 

 admixture. (Vanuxem, p. 48.) 



Place. — Trenton Limestone, after occupying the Isles of Mingan 

 in the Gulf of St. Lawrence, skirts the north shore of that great 

 estuary, with moderate interruptions, as might be expected on such 

 a broken forest-clad coast ; and then, little more than a selvage visible, 

 it passes along the north side of the river St. Lawrence to Montreal, 

 adhering to the metamorphic cliffs by shreds sometimes. On its way 

 from this point to the remote west, it occupies much of the lower 

 part of the Ottawa Valley, all the eastern two-thirds of the north 

 shore of Lake Ontario, in breadths varying from 40 to 80 miles, 

 embraces Lake Simcoe, passes N.W. from thence into Notawasaga 

 and Gloucester Bays of Lake Huron, and forms many islets in the 

 Georgian Bay, the large one of La Cloche among others. From 

 He La Cloche, as a band about ten miles broad, it advances west to 

 the south side of Lake Superior, where it abruptly sweeps round to the 



