172 S. CRUZ, PATAGONIA. [CHAP. ix. 



united. What power, then, has removed along a whole line of 

 country, a solid mass of very hard rock, which had an average 

 thickness of nearly three hundred feet, and a breadth varying from 

 rather less than two miles to four miles ? The river, though it has 

 so little power in transporting even inconsiderable fragments, yet 

 in the lapse of ages might produce by its gradual erosion an effect, 

 of which it is difficult to judge the amount. But in this case, 

 independently of the insignificance of such an agency, good reasons 

 can be assigned for believing that this valley was formerly occupied 

 by an arm of the sea. It is needless in this work to detail the 

 arguments leading to this conclusion, derived from the form and 

 the nature of the step-formed terraces on both sides of the valley, 

 from the manner in which the bottom of the valley near the 

 Andes expands into a great estuary-like plain with sand-hil- 

 locks on it, and from the occurrence of a few sea-shells lying iu 

 the bed of the river. If I had space I could prove that South 

 America was formerly here cut off by a strait, joining the Atlantic 

 and Pacific oceans, like that of Magellan. But it may yet bo 

 asked, how has the solid basalt been moved ? Geologists formerly 

 would have brought into play, the violent action of some over- 

 whelming debacle ; but in this case such a supposition would have 

 been quite inadmissible ; because, the same step-like plains with 

 existing sea-shells lying on their surface, which front the long line 

 of the Patagonian coast, sweep up on each side of the valley of 

 Santa Cruz. No possible action of any flood could thus have 

 modelled the land, either within the valley or along the open 

 coast ; and by the formation of such step-like plains or terraces 

 the valley itself had been hollowed out. Although we know that 

 there are tides, which run within the Narrows of the Strait of 

 Magellan at the rate of eight knots an hour, yet we must confess 

 that it makes the head almost giddy to reflect on the number of 

 years, century after century, which the tides, unaided by a heavy 

 surf, must have required to have corroded so vast an area anc 

 thickness of solid basaltic lava. Nevertheless, we must believe 

 that the strata undermined by the waters of this ancient strait, 

 were broken up into huge fragments, and these lying scattered on 

 the beach, were reduced first to smaller blocks, then to pebbles 

 and lastly to the most impalpable mud, which the tides drifted far 

 into the Eastern or Western Ocean. 

 With .the change in the geological structure of the plains the 



