• MIRAGE. 41 



During the middle of the day, when the earth and the adjacent strata 

 of air had become heated by the almost vertical rays of the sun, we 

 observed, as usual, upon the " Llano estacado," an incessant tremulous 

 motion in the lower strata of the atmosphere, accompanied by a most 

 singular and illusive mirage. This phenomenon, which so bitterly de- 

 luded the French army in Egypt, and has been observed in many other 

 places, is here seen in perfection. 



The very extraordinary refraction of the atmosphere upon these eleva- 

 ted plateaus, causes objects in the distance to be distorted into the most 

 wild and fantastic forms, and often exaggerated to many times their true 

 size. A raven, for instance, would present the appearance of a man 

 walking erect ; and an antelope often be mistaken for a horse or buffalo. 

 In passing along over this thirsty and extended plain in a warm day, 

 the eye of a stranger is suddenly gladdened by the appearance of a 

 beautiful lake, with green and shady groves directly upon the opposite 

 bank. His heart beats with joy at the prospect of speedily luxuriating 

 in the cool and delicious element before him, and he urges his horse 

 forward, thinking it very strange that he does not reach the oasis. At 

 one time he imagines that he has made a sensible diminution in the 

 distance, and goes on with renewed vigor and cheerfulness ; then again 

 he fancies that the object recedes before him, and he becomes discouraged 

 and disheartened. And thus he rides for miles and miles, and still finds 

 himself no nearer the goal than when he first saw it — when, perhaps, 

 some sudden change in the atmosphere would dissipate the illusion, and 

 discloses to him the fact that he had been following a mirage. 



June 21. — On leaving our camp of last night, we crossed the creek 

 and continued a south course for about five miles, when we rose upon 

 the crest of a very elevated ridge which divides the waters of the north 

 from those of the middle or Salt Fork, the valleys of both of which can 

 be seen from this position. Descending upon the south side of the ridge, 

 we encamped upon an affluent of the south fork, which runs rapidly 

 through a narrow valley in an easterly course. The water is abundant, 

 and free from salts. 



The geological formation upon this side of the dividing ridge is differ- 

 ent from that upon the north side, being here a soft, coarse, friable, con- 

 glomerated sandstone, enclosing a small drift of quartz, felspar, mica, and 

 serpentine. The country in this vicinity is much broken and cut Tjp 

 with deep gorges and abrupt ridges, which are mostly impassable for 

 wagons, and we have been obliged in c©nsequence to travel a very cir- 

 cuitous route to-day, keeping the dividing ridges as much as possible, 

 where we invariably find good ground for a road. 



