AGE OF TPIE MASSIVE CRYSTALLINES. 375 



probably be a very conservative estimate of the thickness of the strata, 

 most of which remained as a covering over the crystalline hills until a 

 very recent period. The column embraces a good representation of the 

 entire Paleozoic above the middle Cambrian. 



Age of the massive Crystallines. 



While not wholly pertinent to the theme under consideration, it may 

 not be entirely out of place to touch briefly upon the question of the 

 geological age of the granitic rocks. In the preceding pages it may have 

 been noticed that all specific allusions to their antiquity have been care- 

 fully avoided. Nothing more than the general statement of their pre- 

 Cambrian origin has been offered. The reason is this : there is now a 

 considerable element of doubt that their geological age is really what it 

 has been generally assumed to be. 



All who have had occasion to discuss the granites and porphyries have 

 agreed in assigning them to the Archean. A single possible exception is 

 Van Hise, *, who incidentally states that the granites may be of the same 

 age as the elastics containing or associated with the ore beds of Pilot 

 Knob and neighboring mountains. Haworthf may also have had a little 

 doubt as to the correctness of the references of the granite to the Archean 

 when he states : 



" It is quite remarkable that this comparatively large Archean area should differ 

 so widely from the ordinary Archean rocks of America. Instead of being composed 

 principally of great masses of gneiss and schist, not a single instance of either of 

 these has been found, but in their stead are granites, porphyries, and porphyrites." 



The absence of gneissic and schistose rocks in the massive crystalline 

 area is a noteworthy fact. It is particularly suggestive in the light of the 

 discovery in a deep-well boring near Kansas Cit}^ of real evidences of 

 squeezed rocks. The hole, which was made by a diamond drill, reaches 

 a depth of nearly 2,500 feet. The core at the bottom is li inches in diam- 

 eter. The last 30 feet are reported to be in the rock, which examina- 

 tion shows to be a black mica-schist, the cleavage planes of Avhich have 

 a dip of 35 degrees. If the natural inferences are correct, the entire 

 Paleozoic sequence from the base of the Upper Coal Measures has been 

 passed through in a vertical distance of less than half a mile; the schis- 

 tose floor, upon which rests the unaltered sedimentaries, has been reached 

 in Missouri, and Archean rocks are present which are not unlike the more 

 tyi)ical areas in other parts of the American continent. This being the 



* U. S Geol. Survey, Bull. 86, 1895, p. 504. 

 + Communication. 



