MACKIE — THE GEOLOGY OF THE SEA. 
245 
stones), and argillaceous (clays, shales, &c.) ingredients of our 
eai*tli's crust were generated. 
We arc now brought to tha,t age of remote granitoid or gneissic 
rocks wliich are the oldest presented to us at this liour of the ancient 
primeval strata. These, as it is as well to call by a general name, 
we shall term by theii- Canadian title of " Laurentian." These are 
the rocks which constituted the first dry land above the water — at 
least are the oldest rocks of which any traces remain. 
Now gneiss, in broad terms, may be stated to be regenerated, or 
at any rate modified granite. Its constituent minerals are the 
same ; the like three ostensible substances are there — quartz, felspar, 
and mica. Quartz, one need scarcely say, is one form of sOex, or 
flint ; and mica is a compound of alumina, silica, potash, iron, and 
fluoric acid. It is, however, the felspar which possesses the chief 
interest in our present speciilations. Felspar has an alkaline base, 
either soda or potash. Naturally, therefore, felspathic rocks are 
primarily separated into two sorts — soda-felsjiar and potash-felspar ; 
the other alkali, the volatile ammonia, while linking itself with clays 
and argillaceous earths not entering into any combination, afibrding 
a felspathic product of the two bases, soda and potash, as they occur 
in granitic and gneissic rocks ; the former only exists in a soluble 
state, the potash in its combination producing an insoluhle result. 
No one could describe every piu'pose and aU the phases of even, 
any ordinary object at once, and still more to do so properly we must 
devote something to other objects to which it may be perhaps even 
only remotely related, or with which it may be only casually 
associated. 
If we selected a watch, for example, it would not be sufficient to 
explain that it was an instrument for measuring time, on the 
principle of an uncoiling spring checked in its rate of unfolding 
by a little toothed bar of steel ; the inquiring mind would naturally 
ask for further explanation, and we should thus be led into mechanics 
to explain the principles of the action of the mechanism ; into metal- 
lurgy and jewellery to explain the value and requisites of the 
materials employed ; we should be carried on to clocks and pendulum- 
motions ; and finally onwards still to the general history of the 
methods of measuring the passage of time, from candle-burning and 
