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ROCKS AND MINERALS OF ROCKWOOD PARK. 341 
Physical Geography (Introduction) — Some of the rock 
masses in Rockwood Park go back to tlie dawn of Geologic 
Time, and it is these that have played the most important 
part in moulding the more striking features of its physical 
geography; fully three-quarters of its surface are underlain 
by these ancient rocks. They are of “Laurentian Age” and 
form what geologists call a “Complex” or “Massif,” against 
which later accumulations of sand and clay were ridged up, 
or with which from time to time the “Massif” was covered, 
It would take more time and space then we can here spare 
to go into the particulars of the geological changes that pro- 
duced the “Massif” but we are to understand that the greater 
part of its mass consisted of deposits of mud and sand, laid 
down on the bottom of a primeval sea and subsequently hard- 
ened into solid rock and now further consolidated into lime- 
stones, schists and quartzites. 
Thus we find in the old Laurentain Complex three princi- 
pal varieties of stratified rocks. Into these rocks intruded 
molten matter from the interior of the earth which partly 
fused and broke them up, and which when they reached the 
surface showed themselves as granitic bosses or prominences 
in various parts of the park. 
Many of the beds in these deposits abounded in lime and 
were probably the first to harden, these produced limestones. 
Others were of nearly pure sand, which first hardened into 
sandstones, and later by a cementing together of the individual 
grains, into quartzites. Other beds, in which clay or mud 
was a principal ingredient, were more liable to chemical change, 
and were converted into the schists and gneisses, which form 
a considerable part of the rock masses in the Park. 
