DESCENDING VIEW. 15 



to the terrestrial conditions which preceded them all, and 

 served as the material Germ of their unfolding. 



If we could find a section of the earth's crust in which all 

 the geological stratifications existed in their completeness, and 

 were arranged on horizontal planes, in their natural order of 

 superposition, and if we should then proceed to dig vertically 

 downward through the strata, we would first pass -through 

 layers of loam, fine sand, and gravel, of no very great or very 

 definite thickness. We might find in this deposit the re- 

 mains of plants and animals of existing species, together with 

 the remains of man and of his works. This is the most recent, 

 or what is called the Alluvial Formation. Next we would 

 penetrate an irregular deposit of clay, sand, gravel, and small 

 and large stones, more or less rounded by friction, and which 

 is called the Diluvial Formation. We would next pass 

 through layers of clay, sand, gravel, marl, etc., in greater or 

 less degrees of consolidation, portions of which abound with 

 the remains of animals and plants of species now mostly ex- 

 tinct. These deposits have been roughly estimated as having 

 the aggregate thickness of about thirteen hundred feet, and 

 constitute what is called the Tertiary Formation. Next we 

 would penetrate through deposits of chalk, and strata of marl- 

 stone, ironstone, red sandstone, etc., to the depth of not less 

 than five thousand feet, exhuming, as we proceeded, the 

 remains of huge saurians and other animals of a comparatively 

 low organization, and which became entirely extinct before 

 the next superior formation commenced. These strata, with 

 their distinctive fossils, are comprised in what is called the 

 Secondary Formation. We would then descend through a 

 system of deposites of not less than three thousand feet in 

 thickness, consisting of strata of limestone, slate, ironstone, 

 and mineral coal, constituting what is called the Coal For- 



