262 RECENT FORMATIONS. 



The next class of Recent Formations that falls to be 

 noticed, embraces all such as arise more immediately from 

 Chemical actions and reactions. It is true that chemical 

 changes are incessantly taking place in every formation, 

 whether of aqueous, of organic, or of igneous origin ; but 

 we allude in the present instance to those which, like tra- 

 vertine, sinter, bitumen, and the like, arise from deposition 

 and exudation by mineral springs and other causes chiefly 

 chemical. Every one must have observed how the " petri- 

 fying spring" of ordinary language incrusts the stems, 

 leaves, and stones that lie along its course, the limy incrus- 

 tation thickening with time, and varying in magnitude 

 according to the volume of the spring, and the amount of 

 lime held in solution in its waters. To this set of deposits 

 belong the travertines, cole-tuffs, and calc-sinters of the 

 mineralogist ; and the stalagmites and stalactites found in- 

 crusting the floors and depending from the roofs of caverns.* 

 These calcareous masses are found of all ages, from the 

 incrustations of the present century to the old cave-floors 

 imbedding the stone implements of primitive men and the 

 bones of extinct mammalia cave-lions, cave-bears, hyaenas, 

 mammoths, Irish elks, reindeer, and others, dating back 

 even to the tertiary epoch. As with calcareous depositions, 

 so also with those of a siliceous or flinty nature, which arise 

 generally from hot springs, such as those of Iceland, the 

 Azores, California, New Zealand, and other regions. These 

 siliceous tufas and sinters occur on a less extensive scale, 

 but they accumulate quite in the same manner, and imbed 



* Travertines are light concretionary limestones deposited from waters 

 holding lime in solution, like those of the Arno and Tiber, hence Tibwtinus, 

 Travertinus ; Sinters (Ger. sintern, to drop) are compact calcareous and 

 siliceous incrustations ; tuffs or tufas, on the other hand, are light and 

 porous ; stalactites (Gr. slallaso, to drop) depend from the roofs of calcare- 

 ous caverns ; while stalagmites (Gr. stalagma, a drop) are the more massive 

 incrustations that accumulate on their floors. 



