1834.] EXCAVATION OF THE VALLEY. 185 



though it has so little power in transporting even incon- 

 siderable 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-hillocks on it, and from the occurrence 

 of a few sea-shells lying in 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 be asked, how has 

 the solid basalt been removed ? Geologists formerly would 

 have brought into play the violent action of some over- 

 whelming debdcJe; 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 tlie formation of such step-like plains or terraces the 

 valley itself has 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 and thickness of solid basaltic 

 lava. Nevertheless, we must believe that the strata, under- 

 mined 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 character of the landscape likewise altered. While 

 rambling up some of the narrow and rocky defiles, I could 

 almost have fancied myself transported back again to the 

 barren valleys of the island of St. Jago. Amonjr tl^ 



