Scientific Lectures. 287 



it is called, a country raised but little above the level of the sea, con- 

 sisting of low level areas covered with sand and gravel, which are 

 the meshes in a gigantic net w^ork formed of mountain chains that 

 interlock in every direction. Here the giant cactus flourishes, and 

 that group of prickly and repulsive plants that form the vegetation 

 of deserts. The mountains of this region are volcanic in character, 

 and are destitute of vegetation, but the rocks which compose them 

 assume the most picturesque forms, such as domes, spires, and other 

 architectural figures, and exhibit the most varied and strongly con- 

 trasting colors. The Colorado traverses these mountains through 

 fissures which it has cut in them from summit to base. 



In our exploration of the lower Colorado, we employed a steamer 

 constructed in Philadelphia, and which was put on the river at the 

 lowest stage of water. That was in mid-winter, for the Colorado 

 exhibits the same alterations of level that the Nile does. In the 

 summer it flows with a full and rapid stream, formed by the melting 

 of the snows of the Rocky Mountains, and is fifteen feet higher than 

 in the winter. We chose the time when the water was the lowest, 

 so that the difliculties of navigation should be most apparent. 



After leaving Fort Yuma we entered a terra iiicognita, nothing 

 being then known in regard to the country above that point. We 

 started with sixty days' provisions, leaving the larger half of our 

 party at the fort to await our return, as we expected soon to 

 encounter insurmountable obstacles ; but, at the end of the sixty days, 

 we had navigated the river 500 miles, and had not yet reached any 

 impediment that was absolutely impassable. The boat with which 

 we navigated the river was ingeniously contrived to be unfit for the 

 purpose for which it was intended, inasmuch as it was very narrow 

 and drew three feet of water, when it had the requisite fuel on board 

 for half a day's run. Those who know anything about the naviga- 

 tion of western streams are cognizant of the fact that boats of great 

 capacity are constructed to run on twelve or fifteen inches of water ; 

 but ours drew three feet, and we experienced unnecessary diificulty 

 and delaj^s in getting over tlie rapids and shoals we encountered. 



When near the Great Bend we came in sight of a range of moun- 

 tains, which in its aspects, and in the character of the canon which 

 traverses it, is a fair example of the scenes that we passed through. 

 Day after day as we traveled along, we had seen before us a moun- 

 tainous wall which seemed to block or -way. This was generally of 

 volcanic rock, and almost always of various bright colors, as red, 



