Dr. BiGSBY on the Geography and Geology of Lake Huron. 199 



Several new species of trilobite have been found at St. Joseph's, one of 

 which is represented in Plate XXVII. 



I am obliged to Charles Stokes, Esq. for a communication respecting the 

 specimen fig. 1 : for which see the Appendix to this Paper, page 208. 



The Manitouline limestone is separated on the west and north from that of 

 St. Joseph by waters, low woods, and morasses, nothing being visible near the 

 promontory of the True Detour for many miles around, on the shores of the 

 main^ and of the neighbouring islands, but limestone-shingle, white, slaty, 

 and devoid of petrifactions. On the east the Manitouline limestone is con- 

 nected by a chain of high and rocky islets with Cabot's Head. I have seen 

 numerous specimens from both extremities of this ridge; but it is with Drum- 

 mond. Little Manitou, and the west end of the Grand Manitou, that I am per- 

 sonally conversant. 



Thick vegetation, debris, and the displacements usual in uncultivated coun- 

 tries, prevent an accurate examination of the different successive beds of this 

 chain ; which are to be considered, however, as belonging to one formation, 

 — from their intimate geographical connexion, from their regular horizontal 

 position, and from their containing in distant parts of the chain the same or- 

 ganic remains : but, as is the case with secondary rocks in all parts of the 

 world, their character differs perpetually in places situated on the same level, 

 or even in juxta-position. This limestone is distinguished from that of St. Jo- 

 seph and the north by its greater compactness and hardness, by the difference 

 of its organic remains, and by the sihcified state in which they are found ; all 

 the fossils of Drummond being quartzose or chalcedonic, those of the Little 

 and the Grand Manitou, and of Cabot's Head and its vicinity, being less 

 purely so *. 



This limestone rises usually to the height of 250 feet above the level of the 

 lake, rarely at once in one abrupt precipice, but oftener in confused stair-like 

 ledges. 



The beach at CoUier's Harbour in Drummond Island is in some parts 

 floored with a brown, compact, hard limestone ; almost, if not entirely, devoid 

 of organic remains. It is massive : its surface is usually full of conical cavi- 

 ties, often confluent, about an inch in diameter, and from 1 to 6 inches deep. 

 Their interior occasionally contains a series of similar cavities. A very simi- 



* The substance of the testaceous remains found about Cincinnatus, in the state of Ohio, in 

 parts of Lake Michigan, and in the route from that lake by the Wisconsin river to the Mississipi, 

 consists of fine white quartz. The cellular and chain madrepores, turbinolia;, tubipores, retipores, 

 and shells of the north-east end of Lake Erie, resemble those of Dudley in Staffordshire, and are 

 cherty. 



VOL. VI. 2 D 



