MACKIE — THK HOCKS AND TUKUl TEACHINGS;. 
339 
coaliuually over the same grouud, attain to a perfect understandiug of 
the subject of his study. He must go abroad, either in his o'lvn person 
or equivalently, by making himself acquainted with the travels and 
labours of othci's. Our knowledge of the ancient conditions and 
relations of the oldest rock-masses would not be complete if we limited 
our investigations to those isolated patches in our own country, which, . 
however important, are still only a part of that great whole, more 
important traces of which arc to be met in regions far away. Thus 
those very old — indeed, primitive sedimentary rocks, represented in the 
British Isles in a fragmentary manner, as by the younger or bedded 
gneiss of the Scottish Highlands, assume in Canada and the Arctic 
regions proportions of great extent, and consequently, of far greater 
value. Par back in the obscurity of the past, as must be placed the 
birth-time of these primitive land-masses, we seem, in our first 
investigations, plunged in interminable ignorance, like the explorers of 
some vast subterranean cave in impenetrable darkness. We leave the 
clear evidences of phenomena around us, as we leave the bright sun- 
shine and the miles and miles of gilded landscape vivid through the 
transparent air. All is blank, void ; we know not where to tread ; the 
eye is strained in its efforts to peer through the obscurity until it begins 
to detect, one after another, the slender threads of light that, peering in 
through the cracks and fissures of the roof and walls, are faintly reflected 
from objects around, and in the end we gain a comprehension of the form 
and grandeur of the cavity. 
But the evidence of the primitive lands is not in hopeless obscurity ; 
there may, indeed, be dark and intricate passages, but the broad light of 
Heaven shines on a great deal, and in the mountain-ranges of the world, 
often stand out, bold and high, the memorial pinnacles of the first dry 
land. There is nothing, in reality, to prevent us, by labour and per- 
severance, obtaining a just and accurate conception of the earliest stage 
of the terrestrial and aqueous conditions of our planet, at or before the 
first traces of that succession of animal and vegetable life, which, 
repeatedly adapted to its ever varying states, has descended through 
numerous modifications to our own days. 
"We have learned, already, to distinguish the granites of various 
ages, from primeval to tertiary, from each other ; and we have now 
learned to assort the older or unbedded gneiss, from tlie younger or 
bedded gneiss — the former a portion of the first world, the latter the 
