chap. Yin. Valley of Santa Cruz. 203 



the existing one : the escarpments, also, of the 840 feet 

 summit-plain (with a corresponding northern one, 

 which is met with some way up the valley), appear like 

 the shores of a still larger estuary. Farther up the val- 

 ley, the sides are bounded throughout its entire length 

 by level, gravel-capped terraces, rising above each other 

 in steps. The width between the upper escarpments is 

 on an average between seven and ten miles ; in one 

 spot, however, where cutting through the basaltic lava, 

 it was only one mile and a half. Between the escarp- 

 ments of the second highest terrace the average width 

 is about four or five miles. The bottom of the valley, 

 at the distance of 110 miles from its mouth, begins 

 sensibly to expand, and soon forms a considerable plain, 

 440 feet above the level of the sea, through which the 

 river flows in a gut from twenty to forty feet in depth. 

 I here found, at a point of 140 miles from the Atlantic, 

 and seventy miles from the nearest creek of the Pacific, 

 at the height of 410 feet, a very old and worn shell of 

 Patella deaurita. Lower down the valley, 105 miles 

 from the Atlantic (long. 71° W.), and at an elevation 

 of about 300 feet, I also found, in the bed of the river, 

 two much worn and broken shells of the Voluta ancilla, 

 still retaining traces of their colours ; and one of the 

 Patella deaurita. It appeared that these shells had 

 been washed from the banks into the river ; considering 

 the distance from the sea, the desert and absolutely 

 unfrequented character of the country, and the very 

 ancient appearance of the shells (exactly like those 

 found on the plains nearer the coast), there is, I think, 

 no cause to suspect that they could have been brought 

 here by Indians. 



The plain at the head of the valley is tolerably 

 level, but water-worn, and with many sand-dunes on it 

 like those on a sea-coast. At the highest point to which 



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