198 WALKS AND TALKS. 



erates, quartzites, and marble, all together attaining a thickness 

 of one thousand to six thousand feet. Then come various 

 schistose "rocks and diorites ; and about here occur great beds 

 of haematite or iron ore. This series is four thousand or five 

 thousand feet thick. Next above are black slates and schists, 

 often ferruginous, and other diorites, making about twenty-six 

 hundred feet more. Next, are five thousand feet of mica schists, 

 and finally, several hundred feet of granite and gneiss and kin- 

 dred rocks. These rocks altogether aggregate a thickness not 

 exceeding twenty-five thousand feet. But this may not embrace 

 all. In Canada, Sir William Logan computed the Eozoic rocks 

 as fifty thousand feet thick, and that estimate is generally 

 adopted. The thing of chief importance here, is to know that 

 the thickness is great, and the rocks are all crystalline. 



Now, we explore these old rocks from bottom to top, and 

 scarcely find a trace of organic remains. Who could expect 

 fossil shells or corals imbedded in hard rocks consisting of frag- 

 ments of crystals and grains of quartz, feldspar, mica, and 

 hornblende? The nature of the rock proclaims changes in 

 constitution which must have dissolved or destroyed all relics 

 of the hard parts of animals. Here must be some lost chap- 

 ters of the history of life the first chapters in the volume. 

 It is like the loss of the Alexandrian Library. Could the 

 records of those earliest ages be restored, how many outstand- 

 ing doubts and irresolvable problems would be disposed of! 

 But since the records are wanting since the records may be 

 regarded as lost, we must proceed not as if the records never 

 existed, but by some rational process to reproduce the records. 

 From the bottom of the Cambrian up, we have learned well 

 the general tenor of the history of life. We must project that 

 tenor backward toward a lost beginning. When the death of 

 Dickens, in 1870, left "The Mystery of Edwin Droud" an 

 unfinished tale, it was considered not impracticable to devise 

 concluding chapters which should carry out the tenor of the 

 work as revealed in the written chapters a conclusion which 

 should form a unity with the portion in which the author had 

 divulged his plan and purpose. By the same principles the 



