74 THE SAND STRAND FLOEA 



at Santa Monica. S'and dunes and sand}' fields stretch inland from the 

 beach. The sand is fine and is easily carried by the wind. 



The dunes at Surf, San Diego and some other places in Southern 

 California, as well as those at Point Eeyes and Humboldt Bay, Northern 

 California, and the extensive sand formations in Oregon and Washing- 

 ton are as vet unfamiliar to the writer. 



MEXICO AND CENTRAL AMERICA. 



Mexican Pacific Coast. 



At Mazatlan the sandy Ijeaches occurring near the town were studied. 

 They are very small in extension, but interesting on account of the 

 peculiar red color of the sand. Through erosion from some red cliffs 

 extending into the ocean a sand was formed which was then thrown 

 ashore in quantities. It was very : coarse, and was not carried by the 

 wind. 



The sand at San Bias was also very coarse and of a dark hue, caused 

 by a quantit}' of organic matter being constantlj' brought down with 

 the river and deposited at the mouth, whence waves and wind carried 

 it up on the beach and over the sands. 



West Coast of Chiapas. 



From Salina Cruz southward there is a long sand bank extending 

 as far as the border of Guatemala, at a distance of a few hundred 

 meters to three or four thousand from the coast. This sandbank is in 

 places Cjuite broad, and high dunes are formed. Inside of the bank 

 a long lagoon is formed called the "Estero." Its shores are fringed 

 with mangrove forests. The outer side of the bank is a continuous 

 sandy beach, with a slope of about 35°. The sand is alwa_ys tossed 

 about by the mighty breakers of the Pacific, and the hot tropical sun 

 assisted by the strong winds causes a rapid disintegi-ation of the sand 

 grains, which are cari'ied over the bank and deposited on the estero 

 side, gradually filling the lagoon. The sands of this bank are of a fluvio- 

 marine origin. It is carried down by the numerous rivers that inter- 

 sect the lowlands on the southern slope of Sierra iladre, then taken in 

 hand by the waves and currents of the ocean which distribute the 

 material evenlv along- the coast. 



