VOL. LI.] PHILOSOPHICAL TRANSACTIONS. 455 



be separated in a direction perpendicular to the horizon, if we take any consi- 

 derable portion of it together; but in the horizontal direction, as there is little 

 or no adhesion between one stratum and another, it may be separated without 

 difficulty. Those fissures which are at some depth below the surface of the 

 earth are generally found full of water; but all those that are below the level of 

 the sea must alwa}'s be so, either from the oozing of th6 sea, or rather of the 

 land waters between the strata. 



The strata of the earth are frequently very much bent, being raised in some 

 places, and depressed in others, and this sometimes with a very quick ascent or 

 descent; but as these ascents and descents in a great measure compensate one 

 another, if we take a large extent of country together, we may consider the 

 whole set of strata as lying nearly horizontally. What is very remarkable how- 

 ever in their situation is, that from most, if not all large tracts of high and 

 mountainous countries, the strata lie in a situation more inclined to the horizon 

 than the country itself, the mountainous countries being generally, if not al- 

 ways, formed out of the lower strata of earth. This situation of the strata may 

 be not unaptly represented in the following manner. Let a number of leaves of 

 paper, of several different sorts or colours, be pasted upon one another ; then 

 bending them up together into a ridge in the middle, conceive them to be re- 

 duced again to a level surface, by a plane so passing through them as to cut off 

 all the part that had been raised; let the middle now be again raised a little, and 

 this will be a good general representation of most, if not all large tracts of moun- 

 tainous countries, together with the parts adjacent, throughout the whole world. 



From this formation of the earth, it will follow that we ought to meet with 

 the same kinds of earths, stones, and minerals, appearing at the surface, in long 

 narrow slips, and lying parallel to the greatest rise of any long ridges of moun- 

 tains; and so in fact we find them. The Andes in South America, as it has 

 been said before, have a chain of volcanos that extend in length above 5000 

 miles: these volcanos are probably all derived from the same stratum. Parallel 

 to the Andes is the Sierra, another long ridge of mountains, that run between 

 the Andes and the sea ; and ' these two ridges of mountains run within sight of 

 each other, and almost equally, for above 1000 leagues together,' being each, 

 at a medium, about 20 leagues wide. The gold and silver mines wrought by the 

 Spaniards are found in a tract of country parallel to the direction of these, and 

 extending through a great part of their length. 



The same thing is found to obtain in North America also. The great lakes, 

 which give rise to the river St. Laurence, are kept up by a long ridge of moun- 

 tains that run nearly parallel to the eastern coast. In descending from these 

 towards the sea, the same sets of strata, and in the same order, are generally met 

 with throughout the greatest part of their length. In Great Britain too we have 



