﻿1851.] 



BIGSBY ON CANADIAN ERRATICS. 



229 



find the north shore of this lake (and much of the south shore) 

 bounded almost wholly by similar deposits. These are found from 

 the river Detroit to Long Point (285 miles) in banks and scarps, 

 usually of considerable elevation. 



Sixteen miles east of the river Detroit, the scarps are at least 100 

 feet high. The under portions are greyish blue clay*, both in hori- 

 zontal interrupted flakes, and amorphous ; while the upper parts 

 consist of sand and primitive pebbles, capped with a light-brown 

 loam, which is very fertile. At the western portion of these cliffs 

 (some miles long), the pebbles become boulders ; but at the east end, 

 both disappear, and we have only fine sandf. 



On the beach in front are many erratics, derived from the north of 

 Lake Huron, some weighing several pounds, — greenstone-conglome- 

 rate, porphyry, traps, &c, angular and rolled limestone, together with 

 large quantities of red sand, which the microscope shows to be frag- 

 ments of garnets. 



The beaches on the north-east shore of Lake Erie, west of Grand 

 or Ouse River (240-260 miles east of the last-mentioned locality), 

 are strewn with myriads of dead freshwater shells, accumulated to 

 the depth of some inches. The detritus here (eight miles west of 

 Grand River) does not come from Lake Huron. The preponderating 

 debris is the Medina Sandstone of Niagara. I saw one slab weighing 

 100 lbs., and many smaller and rather angular slabs. They are seen 

 all the way (twenty-four miles) to the Niagara River, with occasional 

 masses of labradorite (Bathurst, &c.) and very large blocks of white 

 crystalline limestone of the N.E. border of Lake Ontario, or of the 

 Ottawa River. 



About the mouth of Grand River, as well as at Long Point, high 

 dunes of loose pure sand occur. These are sometimes very ferru- 

 ginous, and, with occasional intervals, occupied by cliffs of red clay 

 (one of which between one and two miles long occurs three miles east 

 of Grand River), extend to the river Niagara. The red clay contains 

 angular fragments of the local limestone, and rolled primitive blocks, 

 marble, labradorite, and gneiss, as before mentioned. 



There may be ancient terraces belonging to Lake Erie on the 

 north, but I have not seen or heard of any. 



In speaking of the river Niagara, I shall only add a fact or two to 

 the curious details respecting its post-pliocene condition already given 

 us by Sir Charles Lyell and by Mr. Hall, the State Geologist of New 

 York. 



The river-banks of impure clay about the Falls, up to Chippewa, 

 and so on towards Lake Erie (those of Goat Island), are full of small 

 fragments of Niagara limestone, both angular and rounded ; a fact 

 observed all over the valley of the St. Lawrence. Everywhere we 



* This blue clay also covers much of the opposite south coast. 



f Although (after much trouble taken) I could find no shells here, Mr. Whit- 

 tlesey lately discovered freshwater shells, Planorbes and a Helicina, beneath the 

 nearest ridge on the south shore, near Cleaveland ; the ridge is composed of sand 

 or fine gravel derived from the subjacent rocks (Sillim. Journ., New Series, vol. x. 

 p. 31). 



