SURFACE OF THE GLOBE. DISCOVERY OF LEHMAN. 



5 



the old and new continents, some of which rise more than two miles 

 above the present level of the sea. 



It is well known that the water of the sea contains a considerable 

 portion of common salt, and a small portion of other saline ingredi- 

 ents.^ The average amount of salt in the ocean may be estimated 

 at 2 J per cent, of common salt, and J per cent, of other saline com- 

 pounds. 



The atmosphere which surrounds the earth does not come under 

 the attention of the geologist, except as an agent in wearing down 

 the solid surface, by the precipitation of rain, and by change of tem- 

 perature. The inequalities of the earth's surface formed by moun- 

 tains and valleys afford frequent opportunities for observing that the 

 mineral substances of which it is composed are of different kinds: in 

 some situations, we observe strata of chalk ; in others, of sandstone, 

 or compact limestone, or beds of slate, granite, he. It was long 

 since known to working miners, that the different beds of mineral 

 matter lie over each other in a regular order in certain districts, and 

 that certain beds are always found under, and never above, other 

 particular beds. 



The first observations which may be said to have laid the founda- 

 tion for a correct classification of rocks were made by the Germao 

 Lehman, about the middle of the last century. He found that the 

 lower rocks, in some of the mining districts, were distinguished from 

 the upper rocks by their great hardness, and by their structure, which 

 was, for the most part, either crystalline or slaty ; they were also dis- 

 tinguished by the absence of shells and other organic remains, and 

 by the absence of fragments of other rocks, which occur so frequent- 

 ly in the upper rocks or strata. He further observed, that many of 

 the upper strata, besides containing organic remains, appeared to 

 have been formed of fragments of the lower rocks, broken down and 

 agglutinated together ; and hence he inferred, that the lower rocks 

 were formed prior to the creation of animals, and he gave them the 

 name of Primitive or Primary^ and distinguished the upper by the 

 name of Secondary. This grand division, though too hastily form- 

 ed, was of use in the infancy of the science, and induced naturalists 

 to examine more attentively the nature and position of the rocks io 

 different coimtries : and, as their observations became more extend- 

 ed and accurate, a more extended arrangement and classification was 

 found necessary. Many of the earlier geologists maintained that 



* The inquiry has often been made, — Whence did the sea derive its saline con- 

 tents ? It has been supposed by some writers that the salt in the sea has been grad- 

 ually aiigmented by saline particles broiig-ht into it by rivers; but this cause is io- 

 tally inadequate to explain the immense quantity of salt existing in the whole mass 

 of the ocean. If the average depth of the sea be five miles, and it contain 2^- per 

 cent, of salt, — were the water entirely evaporated, the saline residue would form a 

 -stratum of salt more than five hundred feet in thickness covering three fifths of the 

 surface of the globe 



