BASIC INTEUSIVES. 203: 



from scarcely colored needles to those whicli are strongly pleochroic. The 

 pleochroism varies from yellowish for a to yellowish or olive green for Jy, 

 and in many cases to a dark bluish-green for C- In a few cases much of 

 the hornblende has frequently a darker shade in the center than at the 

 border, although of the same color. 



A somewhat different variety of hornblende is observed occupying 

 round to oval areas in the dolerites. This is in tangled aggregates of 

 needles, with which some chlorite is associated. This hornblende is auto- 

 morphic in ^jrismatic zone, ragged at the ends. These aggregates seem to 

 be very coarse, pilitic pseudomorphs after olivine. The areas occupied by 

 these aggregates are similar in appearance to the pseudoamygdules described 

 by Pumpelly as occurring in the Keweenawan lavas. 



The hornblende is largely altered to masses of chlorite and epidote,, 

 usually with the production of some calcite, and to this is due the jjresent 

 extremely chloritic and epidotic characters of many of the badl}^ altered 

 specimens. 



The secondary minerals, chlorite and epidote-zoisite, possess their usual 

 characters. The chlorite is present in very large quantit}-, and next to it 

 the epidote-zoisite is most common. These two minerals make up a large 

 proportion of the rock. In one case porphyritic scalenohedra of calcite- 

 were found in a medium-grained dolerite, the occurrence in every way 

 being- similar to that described in the volcanics of the same region. 



None of the original minerals of these intrusive greenstones give evi- 

 dence of having been severely mashed ; consequently we may safely conclude- 

 that they have not participated in the orogenic movements in pre-Keweena- 

 wan time which have universally affected the older rocks of the Crystal Falls, 

 district. 



RELATIONS TO ADJACENT ROCKS. 



Relations to Lower Huronian Mansfield slates. Thc rclatioU of tllC doleritCS tO the 



Mansfield slate is quite clearly shown along the line of contact between 

 them. This extends from sec. 7 S. to sec. 32, T. 43 N., R. 31 W., on the 

 east side of the Michigamme River, near Mansfield. The presence of 

 numerous large inclusions of the slate in the dolerite and the occurrence of 

 contact rocks in the slate plainly show that the dolerites are younger tlian 

 the slate. Another piece of evidence pointing to this same relation was- 

 found in sec. 28, T. 44 N., R. 32 W. Here was found an angular inclusioiL 



