110 



BULLETIN OF THE 



The relations of these rocks can be well stndied in an adit about one 

 mile long, extending from the western sandstone' through alternating 



"beds of sandstone, conglomerate, and trap, to the ash-bed at the Cop- 

 per Falls mine. We find here that the sandstone, when* underlying 

 the trap, has its upper portion adjacent to it baked and indurated ; 

 showing the usual characteristics of a ferruginous sandstone when 

 subjected to a certain amount of heat. This indurated sandstone has 

 frequently been subjected to secondary water action since it was buried 

 under the trap, and hence has lost some of its hardness and other signs 

 of baking. No fragments of the trap were foimd in the immediately 

 underlying sandstone, but tongues of trap extend down into it in some 

 places, and indurate it. The surface of the trap underlying the sandstone 

 is water-worn, forming smooth, rounded knobs and irregularities, upon 

 ■which the sandstone "was deposited. The immediately overlying sandstone 

 shows none of the baking and induration that the underlying one does. 

 In no case, so far as w*e saw, was there any difficulty in separating the 

 sandstones or conglomerates from the traps. The upper side of the 

 sandstone was especially distinctly separated from the overlying trap, 

 while on the under side, on account of the composition of the sandstone, 

 the junction was not so obvious. While the trap always affected its 

 underlying sandstone, and frequently included "masses of it, in no case 

 did it produce any effect on the overlying one. The sandstones or con- 

 glomerates at their base contain fragments and pebbles of the under- 

 lying trap ; but this detritus diminishes as we recede from the trap, and 

 is generally wanting after a thickness of two or three feet has been laid 

 down. The trap is found to be cellular and amygdaloidal on its upper 

 side, but on the lower to be compact and more coarsely crystalline. If 

 the traps had been intrusive between the beds of sandstone, both the 

 upper and underlying sandstone would be alike affected adjacent to the 

 trap. If the trap was formed from the sandstone metamorphosed 

 in dt'ti there ought to be some gradual passage between the two, and 

 the fragments of sandstone enclosed in the trap should more especially 

 show such passage. On the contrary, nothing of the kind could be 

 found, but the sandstone fragments w^ere greatly indurated, and the 

 traps adjacent to them filled with quartz (64G, G47, G48). Specimens 

 469, 478, 479, 480, 482, and 483 from the Calumet and Heck, and 021 

 from the Copper Falls mine, are examples of the contact of the stuid- 

 stone with the underlying trap, and 477 and 473 from the Calumet and 

 Hecla, and 577, 578, 579, 610, 611, 612, 613, and 620 from Copper Falls, 

 show the contact with the overlying trap. The only explanation of 



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