Ivi. PRESIDENT'S ADDRESS. 



that there was plant-life at the time of their deposition. Lime- 

 stones are made up of the calcareous skeletons of marine animals, 

 and the primitive limestones are in some places thousands of feet 

 thick. The seas of that period held in solution, no doubt more 

 lime and magnesia than they do at present. In the original 

 molten state of the world there was probably a quantity of carbon 

 dioxide present in the atmosphere in a gaseous form. Nothing 

 now can decompose this compound, and reduce it to ordinary 

 carbon, except living plants. Peat beds are composed of the 

 remains of plants which took their carbon from the atmosphere ; 

 and the beds of iron-ore owe their origin to the solvent 

 action of acids produced by vegetable decay. When we 

 take into consideration the immense thickness of the graphic- 

 limestones and iron-ore deposits of the Laurentian beds, and 

 admit the organic origin of the limestones and graphite, we may 

 be prepared to believe that life at that early period was largely 

 developed, though it might have existed in low forms. Fossils 

 were until very recently viewed as characteristics of the beds 

 which contained them. The science of Biology has now found 

 for them another use, by which the unity of the plan of organic 

 creation is illustrated, and an ancestral relationship with living 

 forms confirmed, to which those from the most recent beds show 

 a greater affinity than those of an earlier date. For instance 

 the Pliocene Crags of Norfolk and Suffolk contain 6 per cent, of 

 the mollusca now living, while the later Pliocenes of Italy contain 

 from 90 to 94 per cent. 



The principal fossilizing forces are the decomposition of the 

 less enduring parts of an animal or plant, or an alteration by 

 chemical action, by which its texture is changed, and converted 

 into stone or other mineral. Peat, lignite, and coal are different 

 stages of plants more or less carbonized. Animal remains aie 

 only exceptionally carbonized, such as graptolites and insects in 

 amber, which is an organic medium of petrifaction, and accord- 

 ing to Goeppart, it is the mineralized exudation of extinct conifers. 

 The insects enclosed within it are mainly, if not all, of 

 extinct species, they appear to have been entangled in the thin 



