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the attenuated layers thus produced as coalescing at the edges, 

 forming larger sheets, which, as the process continued, became 

 ever more regular and continuous, developing in succession the 

 different grades of lamination noticed above, and finally ending 

 in the agate-like banding of the most regularly stratified petro- 

 silex. My endorsement of this view extended only so far as to 

 admit the breccia or conglomerate origin of this most schistose 

 variety, which I have long been accustomed to speak of as 

 having a " flattened pebble " structure, or as the " flattened peb- 

 ble " petrosilex ; always regarding the other varieties of banding 

 as original and due to sedimentation. Prof. Hyatt, also, 

 although believing the banding to have resulted in every case 

 from the alteration of the breccia, did not attribute the flattening 

 of the pebbles wholly to compression, but conceived that the 

 elongated appearance might be in part accounted for by the 

 manner in which the finer material or paste was deposited 

 around the pebbles, subsequently uniting with the pebbles so 

 firmly that the outlines of the latter were lost. 



The theory of the conglomerate origin of the banded petro- 

 silex, although presenting at first view, perhaps, a consistent 

 explanation of the phenomena, is, I think, based upon an entire 

 misapprehension of the principal facts. The main point in this 

 theory, viz., that the banded petrosilex and breccia are of the 

 same age, is opposed by the undeniable fact that the latter rock 

 is largely composed of pebbles of the former. In many cases 

 the identity of the breccia pebbles with this variety of petrosilex 

 is clear and perfect ; and where the pebbles are not banded 

 they usually consist of other varieties of petrosilex which have 

 been recognized as existing in this locality, and which are 

 clearly synchronous with the banded rock. The extravasation 

 of portions of the petrosilex through the breccia tells with 

 nearly equal force against the view that they were originally 

 identical. So far as my observations extend, the only evidence 

 of the flattening of pebbles in these rocks is that afforded by the 

 lenticular layers in the schistose petrosilex, or so-called "flat- 

 tened pebble " rock, and this is wholly illusory. These layers 



