100 THE GEOLOGY OP MINNESOTA. 



[Diabase. 



Apatite appears in the midst of the red feldspar, probably not of original crys- 

 tallization, but a result of change consequent on mineralization after the protrusion 

 of the molten mass, during the cooling stage. 



Quartz is not abundant, but is in sizable grains. They are uniformly in the 

 midst of the altered portions of the other minerals, or associated with the red feldspar. 



Four sections examined. 



Meg. Cabotian eruptives of the Taconic. 



Remarks. This rock is thought to represent the intermingling of the basic 

 (gabbro or diabase) magma with the material of the red granites (Nos. IB and 3). 

 The question of the intermingling of these two magmas will be disctfssed in Part III. 



This rock has been called " orthoclase gabbro." The location of the bare knob 

 from which the samples were derived was favorable for the collection of samples by 

 all visitors arriving by railroad from St. Paul. It consequently has been described 

 by several petrographers, and has been considered the type of the Duluth gabbro. 

 Unfortunately Irving fell into this error. At the same time the " hornblende gabbro " 

 of Streng and Kloos seems to be a phase of the same rock, the pyroxene element 

 being replaced largely or wholly by secondary hornblende. Both phases are due to 

 the transformations attendant on the long cooling time, when in contact with the 

 elastics of the Animikie or older rocks. No. 5 is the same rock as No. 1797, and the 

 same as No. 13 of the Minnesota rocks collected by Prof. A. Lacroix in 1888, preserved 

 at the College de France, Paris. No. 5 is also very similar to No. 53B. N. H. w. 



No. 6. DIABASE. 



Duluth. From near the bay in front of the site of the old " Clark house," east of the Spalding hotel, now 

 Covered by buildings and by grading. No. 43 is probably the equivalent of this. By the lake the rock had the 

 appearance of being a wide dike, but No. 43 spreads widely, more in the manner of a general massive. 



Kef. Annual Report, ix, pages 12, 18, 19; Annual Report, x, pages 41, 141; Bulletin ii, page 110; American 

 Association for the Advancement of Science, vol. xxx, page KM. 



Compare Nos. 8, 43 and 53. 



Meg. Medium grained, gray, homogeneous, resembling No. 1C or a fine-grained 

 condition of No. 1. 



Mic. The thin section is much like that of No. 1C, but with less magnetite and 

 with a little quartz. Labradorite, pyroxene (augite), magnetite are also easily 

 distinguished. Apatite spicules are in the quartz. The presence of quartz and a little 

 coloration (reddish) of some of the feldspar grains indicate the effect of the same 

 agencies during the process of cooling, as alreadv mentioned in describing No. 5, 

 although, in general, in the hand specimens collected, such coloration is not distin- 

 guishable. The segregation of the quartz seems to have been shortly preceded by 

 the formation of the apatite spicules, both as secondary products. 



One section examined. 



Age. Probably Cabotian of the Taconic, N. H. w. 



