HOW THE COAL BEDS 



sea. In the early Carboniferous seas the rhizopods, some 

 small as dust, laid down with their tiny shells the founda- 

 tions of mountains yet to be; the "sea lilies'" were at 

 the height of their pride, occupying vast areas in the 

 flowing tide; forms like the present-day nautilus began 

 to appear, and the " lamp-shells " attained their greatest 

 size. The trilobites, hitherto the most conspicuous and 

 noticeable animals of the earth's childhood, were begin- 

 ning to die out, vanquished in the struggle for life by 

 more adaptable forms, and the big sea scorpions were 

 waning fast. The king crabs and the water fleas still 

 throve, and the fishes, though most of them not very 

 large, were growing larger, /some of them taking the 

 appearance of the dog-fish, dome of the ray, some of the 

 shark ; anj}^ what is more important than the fact of 

 size, the /fishes were growing speedier and more capable 

 of attacking weaker creatures. 



In the course of these ages the sea invaded the land ; 

 and shores where land-snails and millipedes and centi- 

 pedes, beetles and scorpions, spiders and cockroaches had 

 found a home became entirely changed, not only in their 

 appearance and character, but in the type which sub- 

 sisted on them. It is possible (for something of the 

 kind has been noticed in our own days in the West 

 Indies, where a sea-crab species is showing signs of 

 becoming a land animal) ^tfaat some of the forms 

 of water animals became used to living in shallower and 

 shallower water as the generations went on till they 

 became partly land and partly water animals amphi- 

 bians, as ~they are called. Thus small newt-like beings, 



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