344 
POPULAR SCIENCE REVIEW. 
tain-ranges^ — tliis was a modification; tlie alteration of old 
sea-beds of sand and clay and sliell-rock into quartzites^ slates_, 
and marble by beat from below^ drawn upwards by the 
thickening masses of heat-conducting sediments above — was 
another; and the side- thrust of intruding granites, and lateral 
pressure from contractions of the earWs crust, — both of them 
producing chemical changes by the heat evolved, and me- 
chanical changes by shifting the particles of the rocky mass 
itself, modified our views still more. And now, whether the 
granites (for they are many) owe their present form and struc- 
ture to heat mechanically produced by lateral thrust, or to 
heat from beneath, they no longer stand as out- cropping 
eminences of a primaeval crust, but as witnesses either of 
extreme changes in the contorted sheets of sediments where 
resistance to pressure was greatest, or of the force of inner 
heat, driving molten rock into the earth^s crust, perhaps 
as the deep-seated foci of old volcanoes, long since planed 
down almost to the base of their clogged up hearth. The 
former notion is sufficient for most cases where the granitic 
boss or axis is the metamorphic ” representative at once of 
all the elements of sand, silt, and lime-rock : whilst gneiss and 
mica- schist and marble-bands represent these matters more 
distinctly, together with graphite for coal-seams, and many a 
combination of two or more of the commonest mineral sub- 
stances (lime, iron, alumina, silica, &c.) to represent the 
whereabouts of organic remains. 
Even vein-granite, syenite, porpyhry, and greenstone are 
included by some among metamorphic rocks, not having neces- 
sarily been produced by dry heat, whether volcanic or plutonic, 
but being possibly the results of hydro-thermal agency 
(water and heat combined), where water confined in the greatly 
heated rocks, by pressure of overlying and laterally crumpled 
strata, has been a strong chemical agent, aided by the alkaline 
salts it contained. 
Nowhere have researches been more systematically carried 
on for threading the almost inextricable maze of ‘‘ metamor- 
phic rocks than in the Laboratory of the Greological Survey 
of Canada; and great results have come from thence. Dr. 
Sterry Hunt, one of the Canadian Geologists, appreciating, 
using, and acknowledging the labours of his fellow- geologists 
and mineralogists of America and Europe, has minutely exa- 
mined and boldly handled these old altered rocks ; and not 
only has he done much in showing their various relation- 
ships to each other and to unaltered sediments, but he has 
offered a comprehensive theory of the successive formation of 
rock-masses, alternately sedimentary and metamorphic, and 
varying in the proportion of contained alkalis, as might be 
