1870.) BROWN—PHYSICS OF ARCTIC ICE. 683 
ever, as new deposits are thrown down, they keep near the surface, 
to be able to get their food ; so that, if to-day a catastrophe were 
to overwhelm the whole marine life of the Arctic regions, it would 
be found (supposing by upheaval or otherwise we were able to 
verify the fact) that the animals would only be imbedded in the 
upper strata of clay, and that the bottom one, with the exception 
of a few dead shells, would be azoic; yet I needjnot say how erro- 
neously we should argue if, from this, we drew the inference that, 
at the time the bottom layers or strata of this laminated clay were 
formed, there was no life in the Arctic waters, or that they were 
formed under circumstances which prevented their being fossiliferous. 
The bearing of this on the subject in question need scarcely be 
pointed out. It ought to be noted that, supposing we were able to 
examine the bottom of the Arctic sea (Davis Straits, for instance), 
it would be found that this clayey deposit would not be found over 
the whole surface of it, but only over patches. For instance, all of 
the ice-fjords would be found full of it to the depth of many feet, 
shoaling off at the seaward ends; and certain other places on the 
coast would be also covered with it; but the middle and mouth of 
Davis Straits and Baflin’s Bay, and the wide intervals between the 
different ice-fjords, would either be bare or but slightly covered 
with small patches from local glaciers ; yet we should reason most 
grievously in error, did we conclude therefrom that the other 
portions of the bottom, covered with sand, gravel, or black mud, 
were laid down at a different period from the other, or under other 
different conditions than geographical position. ‘These ice-rivers 
seem, in the first place, to have taken their direction according to 
the nature of the country over which the inland ice lies, and latterly 
according to the course of the glaciers. No doubt they branch 
over the whole country like a regular river-system’*. When the 
glacier reaches the sea, the stream flows out under the water, and, 
1 Tt may be somewhat superfluous for me to say that these subglacial streams 
are totally different in nature from the streams which flowed in the old water- 
courses found under the drift in various parts of the world. ‘These were 
the beds of the preglacial rivers, and are known to miners as “ sand-dykes,” 
“‘ washouts,” &c. On the North Pacific slope of the Rocky Mountains they are 
very common, and are eagerly sought for by the gold-miners, the “old beds ” 
generally yielding a considerable amount of gold. In California, so thoroughly 
have they been explored by the goid-diggers that, if proper records had been 
kept, a map of the preglacial rivers might now be drawn, almost as detailed as 
that of the postglacial or present river-system. The courses of these ancient 
rivers appear to have been generally in the same direction, and to have had 
their outlets in the valleys near about the same places as the present rivers. 
Sometimes these channels seem to cross nearly at right angles. The old Yuba 
channel, for instance, when its course was interrupted and diverted, ran through 
the site of the present village of “'Timbuctoo,” crossing the bed of the present 
river at Park’s Bar; thence running in a north-westerly course, and falling into 
the Rio de las Plumas (Feather River), near Oroville, a considerable distance 
from its present junction with that river at Mary’sville. These old channels 
exhibit the same windings and precipitous falls as the present river; and they 
have been cut in various places by cafons and ravines; and portions of the older 
deposit, carried down, mingle with the loose gravel and sand detached by more 
recent aqueous action. 
