THE GALLEGOS RIVER. 239 



enormous tides of this coast, which at this point attain to a height of 

 forty-six feet, the second highest in the world and only exceeded by those 

 of the Bay of Fundy. 



Although the entrance to the river at Cape Fairweather is narrow and 

 shallow at low tide, within it becomes broader and much deeper. On the 

 north side, within the limits of the river affected by the tides, there extends 

 a line of high, precipitous cliffs, attaining to an altitude of some four hun- 

 dred and fifty feet. To the southward, extending to and beyond the Rio 

 Chico, there is a low, level, shingle-covered plain, the area of which is 

 still being added to by the action of the tides in the river and along the 

 coast extending southward from the mouth of the latter. The extension 

 of this plain is due to the gradual elevation which this entire coast is now 

 undergoing. While the deposit of shingle, with which the plain is cov- 

 ered, has been and is being formed by the action of the tides, the materi- 

 als for the same have been derived, as already explained, from the Andes, 

 from whence they were transported by the combined action of water and 

 ice, the latter acting in the form of glaciers in and near the Andes and 

 more remotely as icebergs and floating shore and river ice. Thus every 

 agency which has contributed to the formation of the great shingle deposit 

 of Patagonia is still in operation, though, as a rule, they are now much 

 restricted in their effects. The glaciers have receded from the plains, on 

 which they formerly encroached, back into the more remote defiles of the 

 Andes, where they now appear, and in places still descend and give rise to 

 icebergs that now float in the lakes at the bottoms of great valleys, which 

 were once occupied by arms of the sea. While the effects of glaciers and ice- 

 bergs are at present limited to the confines of the Andes, we have already 

 shown, when dealing more particularly with the origin of the Shingle forma- 

 tion, that the areal distribution of each of these agencies was formerly much 

 more extensive. With the breaking up of the ice in the rivers, during each 

 succeeding spring, at the present day vast quantities of bowlders, which, 

 during the winter, have fallen down from overhanging cliffs, and other quan- 

 tities frozen in the ice about the shores and shallower waters, are loosened 

 from the bottom and carried with the floating ice down stream and dropped 

 later, adding their quota to the accumulations which have been going on 

 continuously since the beginning of the final emergence of this region. 



At Guer Aike, some twenty-five miles above the mouth of the Gallegos, 

 the action of the tide ceases, and above this the river assumes its normal 



