LECTUEE IX. 237 



from above or from below bj ladders^ and tbe entrance is 

 sometimes so narrow tliat it requires to be enlarged before a 

 person can pass througb. 



Having thus shortly described the formation of the crevices, 

 grottoes, and caverns, let us glance at their internal condition. 

 Most of these caverns are found in the chalk formation of old 

 and recent origin. The Devonian and carboniferous limestone 

 of Ireland, England, Belgium, and Westphalia ; the magnesian 

 limestone of the Hartz mountains ; the Jura limestone of 

 France, Germany, and Switzerland; the chalk and the num- 

 mulitic masses of the Pyrenees, Alps, and Apennines contain 

 caverns, some of which have acquired sufficient celebrity to 

 attract numbers of travelling sight-seers. What first strikes 

 such tourists is tlie curious form of the stalactites, which by 

 torchhght assume most fantastic shapes. These stalactites 

 are but the crystalline deposits of the trickhng water which 

 hold lime in solution, and they appear brown or yellowish 

 according as the water is impregnated with clay or earth. 

 The size of these stalactites gives no certain clue to their 

 age. The deposits vary even in the same cave according to 

 the quantity and quality of the water. Bones and pebbles are 

 rarely found in the stalactites. This only occurs when the 

 cavern is entirely covered with deposits ; when the stalactite 

 mass forms only a crust in the roof and the walls, but does not 

 hang down in the form of icicles. 



The lime water trickling down from the roof or the walls, 

 forms a crust on the floor of the cave, which, in contra-distinc- 

 tiou to that on the roof, is called the stalagmite crust. Corre- 

 sponding to the spots where a larger quantity of water has 

 trickled down, there are eminences and columns which fre- 

 quently unite with those which hang down from above. 



There are grottoes without stalactites. Such caves as 

 contain but few stalactites are best adapted for further 

 researches. 



Beneath the stalagmite crust are usually found deposits of a 

 so called osseous earth. This is usually a yellowish fatty 

 earth, a clay mixed frequently with sand, often exhibiting a 

 kind of stratified form. In or beneath this clay pebbles are 



