490 



THE AZOIC SYSTEM AND ITS SUBDIVISIONS. 



consistency of this view ; the dynamic simplicity of this view ; and the 

 discovery by the United States geologists of a like series in the Grand 

 Canon of the Colorado. He in no wise meets the direct evidence pre- 

 viously given, that the sandstone and traps are one and the same forma- 

 tion, while, his arguments ignore the mode of formation, i. e. they would 

 be of value only if both the eastern sandstone and the copper-bearing 

 rocks were of exclusively sedimentary origin. (Science, I., pp. 453- 



455.) 



Since so much has been claimed for the Taylor's Falls locality, it will 

 be necessary to pay some attention to the connection of this with the 

 known copper-bearing rocks of Michigan. Beginning at the Nemakagon 

 district, some granites and diabases are found on opposite sides of the 

 Nemakagon River. A thousand feet, below is more diabiise. Abotit250 

 yards south is a small exposure; then, about 100 yards west, another. 

 Four miles northeast is to be found a series of diabase ledges extending 

 for a quarter of a mile. About twelve miles northwest of this is a belt 



" nearly thirty miles in length, over which are scattered, in coraparative pro- 

 fusion bare or slightly concealed ledges. .... With two exceptions— -viz., a 

 sandstone and a conglomerate — ■ the series is formed of trappean rock, mainly 

 diabase and diabase-amygdaloid." 



After passing over an intervening space of about thirty-six miles, dia- 

 base and quartz porphyry were met with in the Clam Falls district. 

 From this locality on there is a scries of outcrops varying from one 

 fourth of a mile to about five miles apart, extending to the Taylor's 

 Falls region (St. Croix district). (GcoL Wise, 1880, III., pp. 399-415.) 



We see then that these rocks, according to the testimony of the Wis- 

 consin geologists, have been mainly determined on lithological evidence, 

 and that when any outcrop of a diabase or mclaphyr was found it was 

 placed without question in the Kewccnawan series. Again, these out- 

 crops are widely separated by drift-covered regions, and thus far the 

 Wisconsin geologists have not advanced the slightest proof that the 

 St. Croix diabase is the same as the Michigan lava flows. 



Dr. Owen stated in rOgard to this locality, that the trap had 



" forced its way through highly fosailiferous strata, breaking up the beds im- 

 mediately overlying it, entangling and partially indurating the fragments, 

 without, however, tilting or metamorphosing the adjacent beds in any percepti- 

 ble degree, The fossils, even of the beds almost in contact with the trap 

 dykes, are in a perfect state of preservation, and the strata themselves have no 

 dip perceptible to the unassisted eye in the hillside where they are exposed." 

 (Geol. Surv. Wise, Iowa, and Minn., 1850, pp. 164, 165.) 



