110 THE STOKY Of THE EARTH AND MAN. 



period, and since this character of the Carboniferous, 

 as well as its varied conditions and products, may 

 excuse us for dwelling on it a little longer than on 

 the others. On the other hand, the immense economic 

 importance of the coal formation, and the interesting 

 points connected with it, have made the Carboniferous 

 more familiar to general readers than most other 

 geological periods, so that we may select points less 

 common and well-known for illustration. Popular 

 expositions of geology are, however, generally so one- 

 sided and so distorted by the prevalent straining after 

 effect, that the true aspect of this age is perhaps not 

 much better known than that of others less frequently 

 described. 



Let us first consider the Carboniferous geography 

 of the northern hemisphere ; and in doing so we may 

 begin with a fact concerning the preceding age. One 

 of the most remarkable features of the Newer De- 

 vonian is the immense quantity of red rocks, particu- 

 larly red sandstones, contained in it. Red sandstones, 

 it is true, occur in older formations, but comparatively 

 rarely ; their great head- quarters, both in Europe and 

 America, in so far as the Palasozoic is concerned, are 

 in the Upper Devonian. Now red sandstone is an 

 infallible mark of rapid deposition, and therefore of 

 active physical change. If we examine the grains 

 of sand in a red sandstone, wo shall find that they 

 are stained or coated, externally, with the peroxide 

 of iron, or iron rust ; and that this coating, with per- 

 haps a portion of the same substance in the inter- 



