AKELEY LAKE PLATE OP THE MESABI IRON RANGE, 1899. U. S. GRANT. 



and it is equally difficult to correct this error as it was the former one, i. e., it is 

 equally as difficult to convince some geologists that they should not all go together 

 into the Animikie. 



Besides the points of difference mentioned by the writer at various places in 

 volumes iv and v (vol. iv, pp. 398, 546; vol. v, pp. 69,- 990-999) between the ores and 

 the containing rocks of the Vermilion and Mesabi ranges, the following further dis- 

 tinctions should be noted between the recognized Animikie ores and those that are 

 involved in the gabbro or its variation, the muscovadyte, in the areas of Plates 

 LXXVII-LXXXI: 



1. The Keewatin ores and rocks dip, in the Akeley Lake area, an average of 

 45, and the Animikie an average of 10, the former becoming almost vertical and 

 the latter almost horizontal (vol. iv, p. 471). 



2. The Keewatin ores are associated with muscovadyte, which is a metamor- 

 phic state of Keewatin sediments, but nothing of the kind is found in the Animikie, 







but only diabase constitutes those sills. Such diabase, when the sills are very thick, 

 acquires gabbro characters, but never muscovadyte characters. The narrowest sill 

 in the Animikie is diabasic; the narrowest in the Keewatin jaspilyte, when thus 

 metamorphosed, is still muscovadyte. 



3. The muscovadyte characters, both in size of grain and in composition, fade 

 out into the enclosing quartzose magnetite layers like an original sedimentary tran- 

 sition, several of the minerals from one side or the other trespassing across the general 

 boundary, but in the case of the sills of the Animikie the transition, observed under 

 the microscope, is distinct and abrupt from igneous rock to clastic. 



4. The ends of the anticline, hypothecated by Dr. Grant (vol. iv, p. 474), have 

 very different lithology, although they both lie on the greenstone, and if both are 

 Animikie they should be almost identical. Compare rocks Nos. 1896 and 879G with 

 No. 1895, described in volume v. One is no more crystalline than the other, but 

 having a different aggregate composition is composed of different minerals and in 

 different proportions. 



Again, these ores are not always contrasted by the titanium content, although 

 the original Keewatin ores are nearly or quite free from titanium. The titanium 

 per cent, apparently, depends on the thoroughness of the metamorphism, and is 

 greatest when the rock was fused. Still, this general difference is remarkable and 

 at present inexplicable. N. H. w. 



