PRESIDENT'S ADDRESS. lv. 



in a large measure laid down in shallow water, and in the neigh- 

 bourhood of land. Their great thickness indicates the enormous 

 denudation which the land areas underwent. Geikie says that 

 the lower half of the Palaeozoic group represents the waste of a 

 plateau cut down to a level 5,000 feet. The Palaeozoic fauna is 

 largely made up of marine invertebrates, in its earlier periods it 

 was entirely so, as far as our knowledge goes, though land- 

 life certainly began before the earliest records which have been 

 as yet discovered. Corals, Echinoderms, Brachiopods, Mollusca, 

 especially the Nautiloid Cephalopods, and the Crustacean group 

 of Trilobites, are the most abundant and characteristic types of 

 animal life. The Cambrian rocks contain no fossil vertebrates, 

 but towards the latter part of the period, Insects, Centipedes, and 

 Spiders were abundant. These appeared somewhat later ; for 

 long ages they were confined to fishes and certain low types 

 allied to them. At the end of the Devonian, and in the Car- 

 boniferous period the Amphibia appeared, followed by the true 

 Reptiles in the Permian age. A very large majority of the 

 Palaeozoic species, and even genera failed to pass over into the 

 Mesozoic. An almost entire change occurred in the larger 

 groups which survived, so that the Corals, Echinoderms, and 

 Fishes are markedly distinct from those which succeeded them. 

 Their difference mainly consists in the greater primitiveness of 

 structure of the older forms. Palaeozoic types stand somewhat in 

 the same relation to succeeding types, as the embryo does to the 

 adult. We may be certain that no living being could have existed 

 when the surface of the earth's crust was glowing hot, or the seas 

 boiling under the enormous atmospheric pressure, which accom- 

 panied their first condensation. These pre-Cambrian rocks are 

 remarkable for their wealth of valuable minerals, and being the 

 foundation, upon which the oldest fossiliferous sediments were laid 

 down. They indicate that vast periods of time had elapsed before 

 the clearly recorded portion of the earth's history began, a time 

 probably longer than all the subsequent periods taken together. 



The Laurentian beds consist of limestones, and iron-ores, and 

 deposits of carbon in a state of graphite or plumbago, indicating 



