THE BEGINNING OF LIFE ON THE EARTH. 27 



Laurentian may be held to afford a strong presumption that, 

 could we discover these rocks in an unaltered state, we should 

 find the limestones filled with marine fossils and the graphite 

 showing the forms or presence of plants. The only startling 

 feature in this conclusion is, that if we admit it, we must 

 also admit that life was developed in the Laurentian time in 

 an exuberance not surpassed, if equalled, in any subse- 

 quent period. Still, there is nothing incredible in this, for 

 if the forms of life were few and low, their increase may 

 have been rapid, because unchecked ; and they no doubt 

 found in the ancient seas a surplusage of material on which 

 to feed and with which to construct their skeletons. Dr. 

 Hunt has estimated that the amount of carbon now sealed up 

 as coaly matter would, if diffused in the atmosphere as carbon 

 dioxide, afford 600 times the quantity of that gas at present 

 floating in the air. A still more vast amount is sealed up in 

 the limestone of the several geological formations. The same 

 chemist has shown that the quantity of lime held in solution 

 in the ocean must have been much greater in Laurentian times 

 than at present. These facts at least allow us to suppose that 

 in the Eozoic times there were great supplies of carbon and of 

 lime available to such creatures of low organisation as were 

 capable of profiting by them ; and we have no reason to doubt 

 that there may have been plants and animals so constituted as 

 to flourish in conditions of this kind, in which perhaps scarcely 

 any modern species could exist. 



These probabilities have caused geologists anxiously to 

 search for any traces of fossil organic remains in the old 

 Laurentian rocks ; and they have been rewarded by the dis- 

 covery of one species, Eozoon Canadense, still often referred to 

 as only a problematical fossil ; but this arises to a large extent 

 from the prevalent want of knowledge sufficient to appreciate 

 the evidence for its organic character. This being once 

 admitted, we have in the existence of Eozoon alone a suffi- 

 cient cause for the accumulation of much of the Laurentian 



