198 On Fossil Crustacea from New- Jersey. 



clay of the isle of Sheppey — in the calcaire grossier of Paris — 

 in the limestone of Pappenheim — and in the tertiary of New- 

 Jersey ; the precise spot seems to be a conglomerate sand 

 strongly tinged with iron. 



It has been remarked by Desmarest, that in geological po- 

 sition the trilobite is older than the Crustacea — but with no 

 great difference of age ; and that the trilobites end, where the 

 Crustacea begin : a remark that will probably be confirmed by 

 the relative position of our own trilobites and Crustacea, if 

 indeed they are to be considered separately. 



A Sketch of the Geology of the Island of Montreal 

 By J. J. Bigsby, M. D. Read Dec. 13, 1824. 



The picturesque and fertile island of Montreal, having 

 close on its north the smaller " Isle Jesus," is situated seventy- 

 six miles above tide-water, in the St. Lawrence, at the con- 

 fluence of that river with the Ottawa. It is chiefly embraced 

 by the waters of the latter stream ; on the north by its small 

 fork, called the " Riviere des Prairies," flowing through low 

 grounds, and occasionally checked by ledges of limestone ; 

 on the west, by its large and irregular expansion, the Lake of 

 the Two Mountains ; on the south by Lake St. Louis,* (in 

 which the two rivers join without mingling) and the rapids 

 forming its outlet, which turn round the great south angle of 

 the island, and pass, with intervals of tranquillity, for eleven 

 miles over reefs and stony shallows ; finally, it is contained 



* Its length passes nearly east and west, and is eighteen miles, by eight 

 miles in greatest breadth. The purplish brown water of the Ottawa occu- 

 pies the half nearest Montreal Island, the line of separation being abrupt 

 and pretty straight. 



