THEIR ECONOMIC PRODUCTS. 97 



may name and arrange them as they may, but the great fact 

 stands unquestioned, that according to our present know- 

 ledge they form the deepest or earliest of the fossiliferous 

 systems. Other fossiliferous strata still deeper and older 

 may be discovered as geology extends her survey of the 

 world's crust, but in the mean time such formations are 

 unknown. Whole systems of strata, deeper and older than 

 the Laurentian, may have been obliterated by metamorphic 

 changes, but such reasoning is altogether futile. In earth- 

 history as in human history we must make our chronologi- 

 cal arrangements according to our knowledge, and the 

 furthest verge to which we have pushed our investigations 

 must necessarily stand as the practical, though provisional, 

 commencement. And, after all, there is something so like 

 a beginning in these old Laurentian rocks, with their lowly 

 eozoa, that we feel, if not at the confines, at least nearing 

 the confines, of the possible in geological history. Observe, 

 it matters nothing to this history though the earth had 

 swung for untold cycles as an incandescent but gradu- 

 ally cooling mass. We have no means of inductively de- 

 termining such a condition, and we are bound in reason to 

 commence our history with the earliest operations we can 

 discover in the crust. The earliest of these operations is 

 the laying down of sediments as nature is now laying 

 down sediments ; and when we find these imbedding forms 

 among the very lowest of organised existence and nothing 

 higher, and find that in after ages the higher gradually 

 make their appearance in orderly succession, it would be 

 abandoning all logical guidance if we did not arrive at the 

 conviction that we were approaching, in these Laurentian 

 quartz-rocks, schists, and serpentines, the commencement of 

 the existing ordainings of our planet. It is true, that Dr 

 Dawson's discovery of worm-burrows in the upper Lauren- 

 tians, if further corroborated, would carry the inference 



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