OLD OCEAN COMMENCES WORK. 63 



boulders of quartz, liberated from its ancient combina- 

 tions and precipitated in the bottom of the sea. Here are 

 boulders of sandstone — vitreous, half-fused sandstone — 

 better known as " hard-heads," which consist of grains of 

 quartz produced by the grinding up of some more ancient 

 quartz rock. These grains have been again cemented to- 

 gether, and a convulsion of Nature has sent them a second 

 time vagrants over the surface of the earth. Here, too, are 

 fragments of those ancient marbles, precipitated at the time 

 when the partners of the ancient chlorides and carbonates 

 formed new copartnerships for life. These all, rounded 

 and battered by long travel, have come from their ancient 

 homes in those northern regions where our continent first 

 raised its head to scowl defiance at the supremacy of tem- 

 pest and flood. They constitute, with numberless speci- 

 mens of rocks of every other age, a grand museum, where 

 every student of Nature may roam and study at his pleas- 

 ure. 



The chemical reactions, and precipitations, and sediment- 

 ary accumulations to which I have referred extended over 

 an immense interval of time. During this long period ma- 

 terials accumulated at the bottom of the sea to the thick- 

 ness of more than twenty-five thousand feet. Their geo- 

 graphical extent corresponded with that of the primeval 

 sea. We find these rocks on every side of the globe, per- 

 forated here and there by the original granitic summits, 

 which serve to point out to us the sites of the oldest isl- 

 ands. For our knowledge of the vast thickness of these 

 older strata, their composition, and their wide American 

 distribution, we are indebted to Sir William Logan and 

 his associates of the Geological Commission of Canada. 

 Sir William has ascertained that this stupendous pile of 

 strata is properly divisible into two great systems, the 

 lower of which he styles the " Laurentian," from the great 



