98 THE PRIMARY PERIODS. 



of Life-beginnings still lower than the lowermost Lau- 

 rentians, and into strata which, in the absence of fossil 

 remains, we are in the habit of designating " meta- 

 morphic ; " but then be it observed that the distance in 

 time between the upper and lower Laurentians is very vast, 

 and that the carrying of lowly life-forms even beyond the 

 Laurentian epoch does not materially affect the conclusion. 

 It is merely believed we are approaching, not asserted we 

 have reached the ultimate limit of vitality. 



Of course everything connected with these investigations 

 is as yet dim and difficult. We know next to nothing of 

 the areas occupied by Laurentian and Cambrian strata, and 

 can only sketch in very general terms the boundaries of 

 the Silurian. We know nothing of the lands from which 

 the Laurentian and Cambrian sediments were borne, and 

 can only dimly indicate the direction from which some of 

 the Silurian were transported. The vast thickness of these 

 formations, the frequent alternations of their strata, and 

 the fineness of the sediments, imply long lapses of time 

 but how long it were in vain, without some standard of com- 

 parison, to inquire and even though we could give the time 

 numerical expression in years and centuries, we could form 

 no adequate conception of its immensity. All that we 

 know for certain is, that the earth in these primeval periods 

 had its seas and continents seas in which sediments were 

 deposited, and lands from which the material must have 

 been borne. With the exception of a few Silurian stems 

 and seed-vessels, we are in utter ignorance of the life and 

 aspects of these lands ; and are merely left to infer the exist- 

 ence of other forms of life from the presence of those we 

 have determined. Of the tenantry of the seas we know that 

 they were few and simple at first, but, as time rolled on, 

 newer and higher types made their appearance, and this 

 not only in greater numerical abundance, but in greater 



