12G 



conglomerates to sandstone, limestone and sliale being sometimes supi:osed 

 to foi'm a basis sufficient to draw well defined lines between rocks of 

 different systems. If, however, we traverse any of our coasts of the 

 present day we find in very limited space the greatest variety of beach. 

 Here we have a stretch of fine sand, passing speedily into grit and 

 soon becoming a x-ough shore covered with loose stones of vaiious 

 sizes, while a little further on, this may possibly, especially near the 

 mouth of some small stream, give jjlace to beds of soft clayey mud. 

 In one place we have a considerable accumulation of sea shells which 

 may, however, be only local, and we may tras'erse long stretches of 

 shore without observing any trace of organic life. Now precisely 

 similar conditions must have, to a great extent, prevailed in early times, 

 and the variously composed beaches of that period have now become the 

 hard stratified rocks which are distinguished by the terms Cambrian, 

 Silurian, Devonian or what not, as the case may be, the fine clay mud 

 becoming shale, which by alteration passes into a hard clay slate, the 

 fine sandy stretch will form a bed of hard sandstone or possibly a 

 glassy quartzite, while the pebbly beach will pass into a conglomerate 

 which may be interstratified, and often is, with beds of shale and lime' 

 stone, and yet all these various kinds of rock are of precisely the same 

 age, notwithstanding their great diversity of character. 



Although we may undoubtedly assume from the advanced type of 

 many of the Cambrian fossils that a long ancestry of earlier forms must 

 have existed, of which the traces have been removed, the fact is patent 

 that the increase in species is wonderfully greater as we advance to more 

 recent periods. From the fossils collected also from all available points 

 on the woi-ld's surface we find that a wonderful uniformity in order of 

 life existed, so that from the strata of New Zealand or Australia pre- 

 cisely the same forms are obtained as are found in the rocks of Great 

 Britain, Norway and Canada to the Kocky Mountains. 



While, however, tlie forms of marine life speedily increased, we do 

 not find indications of land plants till we reach the later portion of 

 the Silurian period. Of sea weeds, however, there was a great abund- 

 ance even in the earlier eras. But in the Devonian period plant life 

 assumed great proportions. The hillsides and marshes were beautiful 

 --.VKith the crreen of that earliest land vegetation. Further we know that 





