SCEXEEY. 87 



far distant as to be below the horizon, are made to rise into 

 view in distorted and chan2:inof outlines. Inverted imao-es of 

 smaller objects, and apparent lakes of clear water, are often 

 seen, and iu\dte the traveller to tm-n aside for refreshment. 

 The first exhibition of mirage that was seen [by Blake's party] 

 was from the margin of the plain at Carriso Creek, looking 

 toward the Gila, about ninety miles distant. It was early m 

 the morning, and the eastern sky had that golden hue which 

 precedes the rising sun. Tall blue columns, and the spires of 

 churches, and overhanging precipices, seemed to stand upon 

 the verge of the plain. Their outlines were changing gradu- 

 ally, and, as the sun rose higher, they were slowly dissipated. 

 After reaching Fort Yuma, and witnessing the strangely pre- 

 cipitous and pinnacled outline of the mountains beyond, it was 

 at once apparent that the mirage consisted of their distorted 

 images. When we were upon the northern part of the desert, 

 the i3eak of Sio-nal Mountain was often distorted and raised 

 .above the horizon. The points of distant ranges also seemed 

 at times to be elevated above the surface, precisely as the 

 headlands of a coast sometimes appear to rise above the water 

 at sea. 



" Many of the phenomena called mirage are not due to re- 

 fraction, but are believed to be the result of reflection from 

 the sand, or smooth surface of clay, or the polished pebbles. 

 The smooth clay forms an excellent reflector for all the rays 

 which are incident at a slight angle, and is most frequently 

 the cause of the appearance of water. The beautiful surface 

 of the pebbly plain may be regarded as a combination of myr- 

 iads of reflectors ; for each pebble is so highly polished, that it 

 reflects lio-ht almost like a mirror. The reflection from such a 

 brilliant surface, w^hen seen at a favorable angle, looks like a 

 sheet of water, the similarity being heightened by the motion 

 of the stratum of heated air in contact with the surface." 



The phenomena of mirage are frequently witnessed in the 

 • Sacramento Basin, and also in the coast valleys, on warm, dry 

 davs. 



