104 



mentary series is of recent origin, and irregularly covering the 

 primary rocks. The shells and corals of the lowest deposit are 

 those which belong to the bordering sea. Scattered over the 

 whole, and at various heights above the sea, from 1300 feet 

 downwards, are recent shells of littoral species of the neighbour- 

 ing coast, so that every part of the surface seems once to have 

 been a shore, thus indicating a very gradual elevation. In this 

 part of the globe we only find irregular recent beds of No. 1. 

 The fossils obtained by Mr. Darwin from the recent formations 

 of Tierra del Fuego and Falkland islands can hardly be distin- 

 guished from species found in the Silurian rocks of England*. 



2. The south temperate. — In the Brazils we find isolated 

 masses of No. 1, with occasionally thin beds of No. 2. In Au- 

 stralia, on the eastern coast, a similar series has been observed. 



3. Near the equator, according to a section made by the writer, 

 embracing the three Cordilleras, the following numbers will re- 

 present the variation in the ascending order : — 



Q f3 3 3 3 



Sedimentary..^ 2 1 2 l s , 3 



Primary 0000000000 



This enumeration furnishes an easy method of indicating the 

 equivalent beds, apart from their relative ages in the different 

 zones, and also the local suppression of some of the series. 



4. North tropic. — The sedimentary rocks of this zone are 

 similar to the preceding, but much more developed. In the 

 north temperate zone these rocks have been well investigated ; 

 and we find in the United States and Europe the following 

 order: — 



f 3 4 4 



Sedimentary . <! 2 3 4 3 24423 



I 1 1 2 1 4 3 12311 

 Primary 000000000000 



Consequently it follows, that although No. 4 (chalk) covers 

 No. 3 (oolite), the latter is not always formed : either of the series 

 may be deposited immediately on the primary base ; and it is 

 necessary to obtain other indications than No. 3 to ascertain the 

 existence of No. 2 under it. However, we know that No. 3 can- 



* Darwin, Voyage of Beagle, p. 253. 



