ACADEMY OF SCIENCES. 229 



on the rocks, and the barometer indicated a depression below the sea-level o^ 

 nearly 100 feet. It is highly probable that further from the base of the moun- 

 tains, the depression would have' been greater." 



E. A. Phelps, assistant engineer, under my directions, has just completed a 

 survey of a route for the branch line of the Southern Pacific Railroad, via San 

 Gorgonio Pass, to Fort Yuma. Mr. Phelps followed along the east side of the 

 valley, while Lieutenant (now Colonel) Williamson's route lay upon the west 

 side. Mr. Phelps's line, on leaving the summit of the Gorgonio Pass, descended 

 •with easy grades a distance of about G.5 miles, where we reach tide-water level ; 

 then descending gradually for 2-1 G-10 miles, to a point on the stage road opposite 

 Dry Lake, where we reach the lowest point but one on the line, being 203 feet 

 below tide ; then with an undulating grade to Salt Creek about six miles, the 

 lowest point in the line, being 215 feet below sea level ; then gradually ascend- 

 ing for about 20 miles, where we rise to the sea level. 



The total length of line below sea level is 50 6-10 miles. The bed of Dry 

 Lake, opposite the stage road, is at least, by estimate, 100 feet lower than any 

 point on our line. 



There is a distinct water line on the eastern slope of the mountains, coinciding 

 with the present sea level, as far as the eye can see, in a southerly direction. This 

 water line or ancient shore line is still more plainly visible on the mountains 

 bordering the western side of the basin. 



The Chowilla valley, lying within .this basin and traversed by our line, is 

 covered with vegetation, such as sage-brush and arrow-weed ; also mesquite 

 trees, which grow from 10 to 30 feet high, and 15 inches in diameter. Water 

 can be found in this valley by digging from 6 to 10 feet, numerous wells which 

 now furnish water having been excavated by the Indians. 



Lieutenant Williamson's report of the west side of the basin and our result 

 down the east &\dr; prove conclusively that a large area of the Colorado basin 

 is below the sea level, sloping gently from the mountains on its border towards 

 the centre, where it reaches a depression assumed to be at least 300 feet below 

 the level of the sea. 



Lieutenant Williamson's elevations were obtained from barometrical obser- 

 vations, while ours were by leveling from the tide waters of San Francisco Bay. 



The elevation of the Colorado river at the crossing at Fort Yuma, was found 

 to be about 117 feet above tide, which coincides nearly with Lieutenant Wil- 

 liamson's barometrical observations. 



Mr. Stearns remarked the great abundance of several species of 

 fresh-water shells, such as Amnicola lo7iginqua, Tryonia protea and 

 T. clathrata, Physa humerosa, and Planorbis amnion ; also Ano- 

 donta (sp.), which are found in a semi-fossil state, in windrows, 

 •within the region referred to by Mr. Gray and Col. Williamson; 

 and which species quite likely may still be found living, in some 

 portion of that country as yet unexplored. The presence of these 



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