Marsh. 1 87 



is flat and marshy, and consists of more recent deposits of 

 alluvium. 



In these gravel and mud beds have been found many re- 

 mains of prehistoric man ; of man, that is, who existed before 

 the earliest civilization of which we know anything, so long 

 ago, in fact, that, in comparison, the 7,000 years through 

 which we are able to trace history back until we reach the 

 early Egyptian civilization, constitute a quite insignificant 

 period. At what time man first appeared on the earth can 

 probably never be certainly determined, but some approxi- 

 mation to the truth may be arrived at by a careful study of 

 the mysterious history which Nature has hidden in the crust 

 of the earth, fragmentary records of which are from time to 

 time brought to the surface. 



Long ages ago our globe was, it is believed, a hot fluid 

 mass, which gradually cooled until its outer crust became 

 solid. In the process of cooling the solid shell became 

 wrinkled, while, at the same time, the vapour by which it 

 was surrounded condensed to form the ocean, which, settling 

 in the hollows, under the action of gravity, left the crests of 

 the wrinkles exposed to the action of those atmospheric 

 forces which we know so well. Frost and snow, running 

 water and heat broke up this exposed surface ; the debris 

 was carried off by streams and rivers, and deposited as 

 sediment on the floor of the ocean, until little by little the 

 original crust was covered with these sedimentary deposits. 

 These being disposed in layers gave rise to what are called 

 the " stratified " rocks, whilst the original crust formed from 

 molten matter constitutes what are termed the "igneous" 

 rocks. From the earliest times until now stratified rocks 

 have been in slow process of formation. You will remember 



