A YOUNG NATURALIST. 



251 



the earth broke through the scarcely solidified crust, and, 

 rushing upward, formed the mountain chains we now see." 



" Then the centre of the earth has been once in a liquid 

 state ?" 



" It is so still, as is shown by volcanoes ; but the period 

 of great catastrophes is past. The molten matter solidified 

 on the surface, as it became cool, and then water made its 

 appearance, and transformed and rendered habitable the thin 

 crust on which we live, the thickness of which is so incon- 

 siderable when compared with the bulk of the globe." 



" What is this molten matter composed of which is burn- 

 ing under our feet ?" 



" The same substances which we see around us — granite, 

 porphyry, and basalts, which are called igneous or Vulca- 

 nian rocks, as contrasted with the Neptunean rocks, such 

 as gypsum or lime, clay and sandstone, the agglomeration 

 of which is attributed to water. The science which deals 

 with these subjects is called geology, a study with which, 

 some day, you will be delighted." 



" Then all Vulcanian rocks can be melted ?" 



" Yes, if they were subject to as great a heat as that ex- 

 isting in the centre of the earth, which reaches an intensity 

 at which the imagination recoils. But to return to the sub- 

 ject of caves. Some have been produced by the dissolving 

 action of water. Thus, at some future date, the spring 

 which we saw gushing out from the fallen mountain might 

 dry up or alter its direction, and leave for the curiosity of 

 future travellers the sight of chambers full of stalactites 

 such as we have inspected." 



Our geological chat was interrupted by an exclamation 

 from PEncuerado, who had just discovered a tree which 

 the Mexicans call " the Tree of St. Ignatius." Its fruit is 

 of a brown color, with a woody husk, something like small 

 melons, which, as they hang on the tree, strike against one 



