BEFORE AND AFTER 73 



probable that, like nearly all later limestones, they are 

 of organic origin. These Archaean rocks cover a large 

 extent of country in Canada. We have some of them in 

 our Islands, in the Hebrides, and north-west of Scotland 

 and in Anglesey, and rising from beneath later rocks in 

 the Malvern Hills and Charnwood Forest.* 



The Archaean rocks are succeeded by the most ancient 

 fossiliferous rocks, the great series called the Cambrian, 

 because found, and first studied, in Wales. They consist 

 of very hard rocks, and contain large quantities of slate. 

 They are followed by another series called the Ordovician ; 

 and that by another the Silurian. These three great 

 systems of rocks measure in all some 30,000 ft. of strata. 

 They form the hills of Wales and the English Lake 

 District. They contain large masses of volcanic rocks. 

 We can see where were the necks of old volcanoes, and 

 the sheets of lava which flowed from them. The volcanoes 

 are worn down to their bases now ; and the hills of Wales 

 and the Lakes represent the remains of ancient mountain 

 chains, which rose high like the Alps in days of old, long 

 before Alps or Himalayas began to be made. These 

 ancient rocks contain abundant remains of living things, 

 chiefly mollusca, crustaceans, corals, and other marine 

 organisms, showing that the waters of those ages abounded 

 with life. 



We must pass on. Next comes a period called the 

 Devonian, or Old Red Sandstone, when the Old Red rocks 

 of Devon and Scotland were laid down. These contain 

 remains of many varieties of very remarkable fish. A 

 long period of coral seas succeeded, when coral reefs 

 flourished over what was to be England ; and their 

 remains formed the Carboniferous Limestone of Derby- 

 shire and the Mendip Hills. A period followed of 



* The older division of the Archaean rocks the Lewisian 

 gneisse consists entirely of metamorphic and igneous rocks ; a 

 later division the Torridonian sandstones is comparatively little 

 altered, but still unfossiliferous. 



