206 C. Lloyd Morgan — Geological Time. 



mathematics will grant to his fellow-labourers in another branch of 

 Science. The evolution of plants and animals (and this is now the 

 only tenable hypothesis of their being) demands time for its 

 fulfilment. 1. In the Wealden Delta deposits we find remains of 

 Pterodactyles, reptiles with a highly specialized system of flying 

 apparatus. 2. As far back as the Triassic epoch, Mammalia, 

 Eeptilia, and perhaps true Aves, had been evolved. 3. In Carboni- 

 ferous times we find that Amphibia with an elaborate dentition 

 (Labyrinthodonta) were in existence and continued without any 

 important modifications until the era of the Trias ; some three or four 

 species of Eeptiles have been found ; and there are representatives 

 of the highly differentiated invertebrate class, Insecta. 4. In the 

 Upper Silurian rocks are the remains of well-developed fish, of 

 Echinodermata (Star-fish), and of a host of Crustacea; while the 

 fossils of the Lower Silurian epoch (especially the Trilobites) were 

 by no means of the lowliest type. 



With regard to the Cambrian rocks, "after quoting Professor 

 Huxley's enumeration of the many classes and orders of marine 

 life (identical with those still existing), whose remains characterize" 

 those rocks. Professor Eamsay writes : " The inference is obvious 

 that in this earliest known varied life we find no evidence of its 

 having lived near the beginning of the zoological series. In a 

 broad sense, compared with what must have gone before, both biolo- 

 o-ically and physically, all the phenomena connected with this old 

 period seem to our minds to be quite a recent description, and the 

 climate of seas and lands were of the very same kind as those 

 which the world enjoys at the present day." 



All this points to a long period of evolution, although, as Professor 

 Huxley truly remarks, that period is measured by the geological 

 clock. We must not however imagine that organic change has been 

 throuo-hout all time uniform in its rate of progress. Climatal 

 changes — alternate periods of perpetual spring and bitter glaciation — 

 and geographical changes in the limits of continental and oceanic 

 areas — now allowing the fauna to multiply freely and expand, now 

 reducing stage by stage a zoological area, and causing the struggle 

 for life to be waged more fiercely — must have caused modification 

 to have at times proceeded with much greater rapidity than we now 

 see around us. But still the "great Phantom of geological Time" 

 rises before us, " springing irrepressibly out of the facts," to use a 

 metaphor of Professor Huxley's, " like the Djin from the jar which 

 the fisherman so incautiously opened, and like the Djin again, being 

 vaporous, shifting and indefinable, but unmistakably gigantic." We 

 may not yet be able to read the time accurately by our geological or 

 biological clock, but that clock for all that is no plaything. 



There is one more aspect of this great question which remains to 

 be considered. We have seen that there is a theory to account for 

 the cold of the Glacial epoch, on the supposition that it was during 

 periods of great excentricity of the earth's orbit that the glaciation 

 took place. If then we could ascertain at what period the excen- 

 tricity which produced the Glacial epoch occurred — if this hypothesis 



