STRUCTURAL RELATIONS OF PRE-CAMBRIAN AND PALAEOZOIC. 
7 
slope of the hill is very steep. The exposed crest of the ridge is 
granite, but patches of limestone overlie the granite a very few 
feet below the highest point. On the west slope most of the lime- 
stone cover remains, the beds nearest the granite often adjusting 
themselves to its slope. At Kingston Mills, 5 miles northeast of 
Kingston, a railway cut just west of the canal affords an excel- 
lent exposure of the contact between the Ordovician limestone 
and the Archaean. The steep slope of the Pre-Cambrian hill 
surface exposed in this cut is shown in Plate II, A. There is 
no residuary clay between the Archaean and the Palaeozoic, but 
the limestone at the contact includes coarse angular sand and 
gravel of quartz and feldspar, and boulders of granite similar to 
the one exposed on the north side of the cut at Kingston Mills 
are of frequent occurrence. The largest of these boulders which 
has been observed occurs in the basal beds of the Trenton in the 
Jacques Cartier river at Pont Rouge, Quebec. It has a maximum 
length of 8 feet 4 inches and rises 2 feet above the partially en- 
closing horizontal limestone strata (Plate II, B), which dip away 
at angles of from 15 to 20 degrees in the immediate vicinity of 
the boulder. The fresh character of the Pre-Cambrian surface 
and the absence of residuary clays at its contact with the over- 
lying Palaeozoic are in marked contrast to the conditions re- 
ported in Wisconsin where deposits of clay 10 to 20 feet thick 
and consisting of decomposed Pre-Cambrian rocks separate the 
Cambrian from the Pre-Cambrian. 1 
Throughout a considerable area of the Pre-Cambrian rocks 
northwest of the head of the St. Lawrence the orientation of the 
lakes and streams conforms largely to the strike of the highly 
inclined Archaean rocks. The strike valleys are doubtless chiefly 
the product of Pre-Cambrian erosion in beds of softer schists or 
zones of inter bedded crystalline limestone, although they are now 
partially filled by drift and may have been somewhat modified 
by glacial action. 
The foregoing summary of the observations and opinions 
offjvarious geologists regarding the character of Pre-Cambrian 
topography in Ontario indicates that the transgressing seas of 
1 S. Weidman, Jour. Geol., Vol. XI, 1903, p. 311. 
