GEOLOGY — CAUSE AND EFFECT OF LOW TEMPERATURE. 43 



holding, as they do, such peculiar and constant relation to the areas which are drained through 

 them, cannot possibly he regarded as rifts formed by volcanic action in the barriers which they 

 traverse. The conclusion seems irresistible that they have been formed principally, if not 

 entirely, by currents of water, of which the present streams are representatives. 



Another of the deeply graven records from which we are attempting to deduce the ancient 

 history of the western coast is found in the great depth of the channels by which these streams 

 terminate in the Pacific. The deep and narrow fiords which mark the northern portion of the 

 western coast, of which those opposite the island of Vancouver, on the coast of Washington 

 Territory, are good examples, have been described by Professor Dana, in his Geology of the 

 Exploring Expedition. The mouth of the Columbia exhibits similar features. For a hundred 

 miles it forms an arm of the sea of great and uniform depth. 



The channel of the Golden Gate has a maximum depth of nearly fifty fathoms, being greatest 

 immediately in the line of the axis of the chain through which it is cut, while the bar without 

 and the bay within are silted up to within less than ten fathoms of the surface. 



The Straits of Carquines have a maximum depth of eighteen fathoms, and in the line of the 

 range which bounds them an average depth of fourteen. 



It is evident that glaciers could now be formed in the Cascade mountains only by a great 

 depression of temperature, and it is perhaps doubtful whether glaciers would now form to the 

 extent indicated by the traces of their former existence, which has been described, even with a 

 depression of temperature so low as to precipitate and congeal all the vapor which floats above 

 them. Without, however, raising that question, we may be at least certain that with the former 

 existence of glaciers in the Cascades, the average temperature was much lower than at present. 

 This must have been dependent upon one of two causes : either a great and radical difference in 

 the climate of the coast without a change of elevation, or, the climate remaining the same, by 

 the elevation of the coast to a general altitude several thousand feet higher than at present. 



Of the condition required by the first of these hypotheses we have no other evidence than that 

 of the glaciers themselves, while of the former elevation of the coast, in the sub-asrial excavation 

 of the fiords at the north in the deep channel of the Columbia, and, as it seems to me, in that 

 of the Golden Gate, we have cumulative and conclusive proof. The effect of such an elevation 

 as would be required to cover the slopes and valleys of the Cascades with glaciers, would be 

 exhibited in various ways. The amount of moisture precipitated upon the sides of these moun- 

 tains would then be much greater than now. Instead of presenting isolated peaks rising above 

 the line of congelation, they would form an unbroken wall, of which the summit, white 

 with perpetual frost, would rob of all its moisture the wind, then as now, blowing over it from 

 the Pacific. This precipitation, though greatest on the western slopes, and forming by its con- 

 gelation sheets of ice which would reach far down its sides, crowding themselves into the 

 angular valleys which now lead toward the Pacific, would also extend its influence to the eastern 

 slope, fill many of its basins, now dry, with water, give greater volume and efficiency to the 

 streams, and enable them to score so deeply the surfaces of the plateau, and force mountain 

 barriers to reach the ocean, cutting deep channels in its shores where we now find them. 



