MANUAL OF NATURAL HISTORY. 587 



come larger and wider, the apex of the triangle 

 always pointing up the rivers. Estuary deposits 

 are formed by the mud, sand, and vegetable matter 

 brought down by the rivers. The bones of animals, 

 and plants of the interior, are often found in these 

 deposits ; as those of the Elephant and Tiger at the 

 mouth of the Ganges ; those of the Camel and Cro- 

 codile at the mouth of the Nile ; those of the Hippo- 

 potamus, the Rhinoceros, and the Giraffe, at the 

 mouth of the Niger ; and those of the Buffalo and 

 Elk at the mouth of the Mississippi. Lacustrine 

 deposits are beds formed in lakes, morasses, and 

 swamps, producing heaps of shell-marl and peat-moss, 

 clay-slate, and rolled pebbles, with remains of fresh- 

 water fishes. The prairies of North America, the 

 pampas of South America, and the steppes of Europe 

 and Asia, were, most probably, lakes, filled up by these 

 accumulations ; bones and horns of deer, horses, bears, 

 beavers, and foxes, are found in these deposits. Mi- 

 neral deposits constitute all aggregations of mineral 

 and saline matter, derived from the action of springs, 

 forming crusts of various substances, as the stalac- 

 tites and stalagmites of Derbyshire, and the grotto 

 of Antiparos. Tufa, or travertine, is a deposition of 

 lime, as in cold springs, where it forms calc-spar, and 

 in hot springs, where it occurs in the form of arra- 

 gonite. These springs are often made to incrust 

 various objects, thus producing false fossils. Hot 

 springs, as those of Iceland and in the Azores, depo- 

 sit silex on cooling, which is called tuff or sinter; 

 opal is also formed in this manner. Ferruginous 



