OUTLINES OF GEOLOGY. 



33 



73. Calcareous formations of this order take the form of 

 stalactite and stalagmite, of pisolite, and of travertine ; they 

 also occur in masses of alluvial sand and gravel, which they 

 convert into silicious limestone, and calcareous pudding 

 stones. All such formations are due to the solution of 

 carbonate of lime, in water containing excess of acid, and its 

 subsequent deposit, as that excess escapes. 



Travertine is a carbonate of lime which occurs in concre- 

 tions of agranular structure, or even, occasionally, crystaline. 

 It is sometimes so firmly aggregated as to be liable to be 

 mistaken for rocks of far more ancient date. 



These calcareous formations are partly cotemporaneous 

 with the alluvial, and partly of more ancient date. The 

 latter we shall have occasion to speak of hereafter. Of such 

 as are at present going forward, we may cite the following 

 instances : — 



1. Travertines forming in Italy, as cited by Davy, in his 

 " Consolations in Travel." 



2. A travertine forming near Batavia, in Java. 



3. Travertine forming in the marshes of the great plain 

 of Hungary, which becomes sufficiently solid to serve as a 

 building stone. It contains shells which are unaltered, and 

 belong to the species found at present living on the spot. 



4. A calcareous rock, containing shells and aquatic vege- 

 tables, which is daily making at the bottom of a lake in 

 Scotland. 



5. Innumerable instances of stalactite and stalagmite in 

 grottos. 



Such formations are not confined to the land, and to fresh 

 water, but are taking place in the ocean, or in lands recently 

 conquered from it. 



Of this we have proof : — 



1. In the concretions forming in the Mediterranean, oppo- 

 site Messina. Here the beach, which is a sand, composed of 



