PREVIOUS TO THE LAST GEOLOGICAL REVOLUTION. D 



clay, particularly gold, vrhich is often in sufficient quantity to 

 be worked. The same conglomerate is likewise found in the 

 caves, and contains the same animal remains as the red clay ; 

 so that there can be no doubt of the contemporaneousness of 

 their formation. These most recent formations are found in 

 the caves, under all the conditions I have thus attempted to 

 describe, and in about the same relative proportions as to 

 quantity ; the red clay soil being by far the most common, ei- 

 ther in a piu-e state, or mixed with siliceous boulders or gravel. 

 But all these kinds of soil have undergone changed since their 

 deposition in the caves, of which changes I will now proceed 

 to give an account. 



The first change arises from the infiltration of water charged 

 with lime. The lime derived from the evaporation of the wa- 

 ter, and its contact with the surrounding hard bodies, unites 

 the loose particles of the soil, and changes the whole into a 

 mass as hard as stone. Indeed, the looser the soil was pre- 

 viously to this infiltration, the harder does it afterwards be- 

 come, fi:om the greater quantity of calcareous particles which 

 it allows to penetrate. For this reason the fine yellow clay 

 never becomes so hard as the coarse red, the loose composi- 

 tion of which even permits the calcareous incrustation to col- 

 lect in connected masses, which are sometimes solid, at other 

 times contain holes lined with beautiful small crystals of cal- 

 careous spar. Lastly, the beds of boulders and gravel, which 

 outside the caves are loose and unconnected, are metamor- 

 phosed into perfect pudding-stone inside. Another character 

 which distinguishes the soil within the caves from that with- 

 out, is the much greater quantity of fragments of limestone 

 contained in it. These fragments have their angles partly 

 sharp, and partly broken off and rounded ; and are from the 

 most trifling size up to that of immense blocks. In those 

 caves the opening of which is to the north, and which are 

 closed at the end, these fragments are found in extraordinary 

 abundance, especially in the inner part, towards the bottom : 

 while in those which open to the south, or have two opposite 

 entrances, the fragments are either entirely wanting, or occur 

 in trifling quantities. This result is based upon the exami- 

 nation of so many caverns, that it cannot be looked upon as 

 an accidental circumstance : and the natural explanation ap- 

 pears to be, that the inundation which deposited the soil in 

 these caves, must have moved from north to south, and with 

 sufficient force to carry along with it the blocks of all sizes 

 which we see scattered inside and outside of the caves. 



But the most important substance which has enriched the 

 soil since its deposition, is, without doubt, saltpetre, which is 



