Situation of Zones without Rain, and of Deserts. 373 



©f a deep blue colour ; but if some clouds occur at tbe setting 

 of the sun, they are ornamented with the most beautiful tints 

 of green, purple, and violet, so that the scene then possesses 

 an extraordinary beauty. If to this we add, that rain, during 

 a serene sky, is pretty frequent in the Gulf of California, we 

 shall perceive that there is a series of effects derived from a 

 particular state of the aqueous vapour dissolved in the air, 

 whose more minute examination is well worthy of the atten- 

 tion of navigators. 



To the east of Lower California, and beyond the break in 

 the continuity of the land, produced by the Gulf of California, 

 there rises the vast undulated plateau of Mexico, which sinks 

 rapidly on the opposite side in Cohahuila and Texas, to which 

 succeed the low land of New Orleans and the Floridas, washed 

 by the warm waters of the Mexican Gulf. These varieties 

 of configuration must necessarily produce abrupt variations in 

 the climate ; and these affect the transition of the hemi- 

 annual rains of summer into those of winter ; so that a certain 

 degree of attention is necessary to follow these different ar- 

 rangements, and the following are the complications, whose 

 existence observation has enabled us to ascertain. 



According to the information communicated to me by M. 

 Duport Saint Clair, the district of Cinaloa, situated opposite 

 to Old California, possesses estival rains, which become rarer 

 towards the north in Sonora, whei'e they are very feeble, and 

 very irregular. Beyond Guaimas, in lat. 28° N., a week often 

 passes without any thing falling but a trifling shower ; but this 

 season is prolonged until December, when one or two tropical 

 rains take place, wliich cause the rivers to overflow, and 

 from that time these rains cease completely until June: in 

 Sonora, between 27° and 32'' N., the air is said to be generally 

 healthy and salubrious, excepting on the coast; further to- 

 wards the north, there are the fogs and irregular rains of 

 Monterey, in New California. 



On the plateau of New Mexico, in the same latitude as 

 Central Persia and ^yvi2L, there are very intense colds ; snow 

 is sometimes seen to fall at Mexico in lat. 19'' 25' at the height 

 of 7400 feet ; nevertheless, this circumstance does not destroy 

 the arrangement of the summer intertropical rains, although 



