THE EVOLUTION OF CONTINUITY 159 



Sections. Systems. Nature of Rocks. 



Primary or 

 Palaeozoic 



' Permian Sands, limestone, slate 



Carboniferous Coal, limestones 



Devonian Old red sandstone 



. Cambrian } Sands « S rave1 ' shale » 8lato 



Archaaan Archaean Granites, schists 



Sandstone, limestone, and chalk strata have been laid 

 down at the bottom of the sea, or on the beds of inland 

 lakes, during immense periods of time, and have been derived 

 from the siliceous skeletons and calcareous shells of endless 

 generations of marine organisms. Shales and slates, which 

 are practically indurated muds, have also been deposited 

 under water, but presumably shallow water at the mouths 

 of rivers and estuaries. The origin of coal measures from 

 palaeozoic vegetation is common knowledge. 



There is clear proof that from time to time in the past 

 there have been great elevations of the sea-bed above water 

 level, alternating with subsidences, for we find the Devonian 

 old red sandstone of submarine origin followed by the 

 carboniferous system representing ages of terrestrial plant- 

 life, and this in turn followed by the submarine deposition 

 of sands, limestone and chalk. Elevation has alternated 

 with subsidence. Our knowledge of the forms of lif e abound- 

 ing in past ages is gathered from the fossils found in the 

 various strata, and it is noteworthy that from below upwards 

 there is an increasing complexity of type. In certain layers 

 new organisms suddenly appear as if their evolution had 

 been a sudden process, while others plentiful in lower strata 

 may completely be wanting. 



But, while this is so, we do not find the successive 

 Continuity-types appearing with successive strata. On the 

 contrary, we find that as far back as the Silurian period 

 segmental Individuals were in existence. In the Silurian 

 rocks fossils have been discovered of Algae, Hydrozoa, Corals, 

 Starfish, Crustaceans, Brachiopods, Cephalopods, Insects, 

 and Fishes. That is, at this comparatively " early age " 

 all the forms of living Continuity had evolved. If we accept 

 the Cambrian system as the first of the earth's crust, we 

 would naturally conclude that evolution was a more rapid 

 process when the world was younger than in later ages ; 



