20 EVOLUTION IN THE PAST 



Hearts were scarcely formed. In many groups there were no 

 separate sexes. Brains were rare, and headless life abounded. 

 Indeed, so far as evidence goes, the little shrimp-like forms 

 and the winged snails alone relieved the prevailing inertia. 

 LAND LIFE The rocks tell nothing of life on land, and, so far as is 

 known, it breathed as yet only in the waters. But there 

 can be little doubt that a humble land - vegetation was in 

 process of development. Some forms of algae from salt and 

 fresh waters may well have crept over the land, and even 

 found their way to far up-country scenes. Indeed, funguses, 

 liverworts, and even club-mosses and " horsetails " of primi- 

 tive character, may have flourished far and wide ; for, to 

 judge by the plants of subsequent Periods, many steps must 

 have been taken before the close of the Cambrian in the 

 evolution of a land- vegetation. Possibly the land air was 

 still unfit for animal breathing ; but the carbon-absorptions 

 of plant-life were slowly rendering it less choking and op- 

 pressive. 



Long gone though be the Cambrian world, its scenery is not 

 wholly past recall. There can have been nothing peculiar 

 in the appearance of the sea ; for, however much its in- 

 habitants have changed, the general aspect of its waters must 

 have been the same as now. Nor can the landscapes have 

 been very different from scenes still to be found in many 

 regions of the Earth; vast ranges of mountains, active 

 volcanoes, wide rivers rushing along laden with sediments ; 

 and hill-sides, valleys, and plains scantily clothed with a 

 flowerless vegetation. 



The air, no doubt, was excessively humid ; and thick 

 mists must have been frequent over land and sea. As regards 

 life it was a world of silence ; for the stillness was broken 

 only by tempests, volcanic eruptions, and other disquietudes, 

 of inanimate Nature. 



