EXAMPLES OF THE GEOLOGICAL PAST 171 



were buried to become our coal seams of commerce. Here and there 

 a few others have been found in older strata but it is not until the 

 Tertiary that their remains were found in any quantity. 



During this period or era, the configuration of the earth was 

 steadily approaching that of the present day, but there still existed 

 a great equatorial ocean, while East India and Africa, Australia and 

 Asia, North Europe and America were probably united by land con- 

 nections. The faunas of the planet also approached their present 

 state, and might have continued to expand more broadly, had it not 

 been for a rapid lowering of the earth's temperature, which brought 

 about a great glacial period. 



Spring-tails of the present day live in moss, under logs or fallen 

 leaves, in grass, on water, snow, or in almost any place that is suf- 

 ficiently damp. Their mouth parts are hidden and very difficult to 

 study, but the insects are doubtless vegetable feeders like their 

 Bristle-tail relatives. 



Millions of years ago the latter probably fed on water-soaked seeds 

 or other vegetable matter of a starchy nature, but today they inhabit 

 the houses of man, feeding upon the paste which keeps our wall 

 papers in place, or upon the same substance, w r hen it may be found, 

 in the bindings of books upon our shelves. It is a strange habit in- 

 deed, to acquire upon one's Nth millionth birthday as a race! 



Another creature, still existing, whose kind may be traced like the 

 Aptera, far into the geological past, is the inappropriately named 

 wood-louse. In reality a terrestrial crustacean closely related to 

 the land crabs and not an insect in any sense of the word, this little 

 oniscus is familiar to everyone living in the country' who has ever 

 turned over a stone or log or a bit of decaying wood. 



Members of the Isopoda are represented in all seas and lands, the 

 wood-louse being the only land-loving representative of the order. 



