CHAPTER VI. 



DISCUSSION OF GEOLOGICAL PHENOMENA, 



In the last two chapters the observations gathered have been pre- 

 sented in the form which it was supposed would be most useful to the 

 geologist or miner who wished to study the region itself. For those who 

 have no occasion to examine the actual ground, it may be well to present 

 concisely and in a generalized form some of the more suggestive facts ob- 

 served, in a geological rather than topographical order, which will be the 

 object of the following pages. 



SEDIMENTARY ROCKS. 



Archean. That Archean land masses must have existed during the dep- 

 osition of the Paleozoic and Mesozoic beds found in this region is abun- 

 dantly proved, aside from all structural evidences, by the occurrence at vari- 

 ous horizons, in beds evidently of littoral formation, of rolled grains and 

 pebbles of Archean rocks. Among these grains and pebbles that which 

 would best resist abrasion, quartz, forms naturally the larger proportion, but 

 granite and even gneiss are found, and, among the finer materials, feldspar 

 and mica often form a large proportion of the sandstones. It is further 

 noteworthy that these pebbles do not differ in character from the present 

 Archean rocks ; in other words, afford no evidence that the latter have been 

 changed by metamorphism since the Cambrian epoch. The fact that only 

 .at one point, and this close to a supposed shore line, is any but the charac- 

 teristically lowest bed of the Cambrian found in contact with the Archean, 

 ehows that the upper surface of the latter, or the bed of the Cambrian ocean, 



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