140 THE STORY OF THE EARTH AND MAN. 



US. If these are really the oldest land snails, it is 

 curious that they are so small, — so much inferior to 

 many of their modern successors even in the same 

 latitudes. The climate of the coal period must have 

 suited them, and there was plenty of vegetable food, 

 though perhaps not the richest or most tender. There 

 is no excuse for them in their outward circumstances. 

 Why, then, unlike so many other creatures, do they 

 enter on existence in this poor and sneaking way. 

 We must here for their benefit modify in two ways 

 the statement broadly made in a previous chapter, 

 that new types come in under forms of great magni- 

 tude. First, we often have, in advance of the main in- 

 road of a new horde of animals, a few insignificant 

 stragglers as a sort of prelude to the rest — precursors 

 intimating beforehand what is to follow. We shall 

 find this to be the case with the little reptiles of the 

 coal, and the little mammals of the Trias, preceding 

 the greater forms which subsequently set in. Se- 

 condly, this seems to be more applicable in the case of 

 land animals than in the case of those of the waters. 

 To the waters was the fiat to bring forth living things 

 issued. They have always kept to themselves the 

 most gigantic forms of life ; and it seems as if new 

 forms of life entering on the land had to begin in a 

 small way and took more time to culminate. 



The circumstances in which the first specimens of 

 Carboniferous snails and gally-worms were found are 

 so peculiar and so characteristic of the coal formation, 

 that I must pause here to notice them, and to make of 



