THEORY OF THE EARTH. 31 



ties of slime and sediment into harbours and 

 creeks ; into all places, in short, where its waters 

 are more tranquil than ordinary. The currents 

 also heap up at their meeting, or throw out at 

 their sides, the sand which they are continually 

 raising from the bottom of the sea, forming it in- 

 to banks and shallows. 



Stalactites. 



Certain waters, after dissolving calcareous sub- 

 stances by means of the superabundant carbonic 

 acid with which they are impregnated, allow these 

 substances to crystallize after the acid has evapo- 

 rated ; and, in this manner, form stalactites, and 

 other concretions. There are strata, confusedly 

 crystallized in fresh water, which are sufficiently 

 extensive to be compared with some of those 

 which have been deposited by the ancient sea. 

 The famous Travertine quarries of the neighbour- 

 hood of Rome, and the rocks of the same sub- 

 stance, which are formed, and continually varied 

 in figure, by the river of Teverona, are generally 

 known. These two modes of action may be com- 

 bined ; the deposits accumulated by the sea may 

 be solidified by stalactite. Thus, when springs 

 abounding in calcareous matter, or containing 

 some other substance in solution, happen to fall 

 into places where these deposits are formed, we then 

 find aggregates in which marine and fresh-water 



