STRUCTURAL GEOLOGY. 



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The feldspar masses.] 



The removal of the superficial portion of the gabbro batholyth left exposed to 

 atmospheric action the body of the gabbro mass. It is not probable that this move- 

 ment took place within the crust below the surface. The effect of atmospheric con- 

 tact is visible in many places on this diabase, and the crystallization of the red rock 

 in nearly all cases is not that of deep-seated congealation. The fact that what 

 is left of this great sheet seldom exhibits distinct superficial phenomena can 

 be attributed to the denudation of its accessible upper portions, and the same 

 probably applies to explain the present condition of the surface of the gabbro area 

 itself. 



The feldspar masses, or " anorthost/tc." The former of these terms seems to be 

 preferable to the latter, because the term anorthosyte is quite extensively applied to 

 the gabbro mass itself; whereas, the objects here intended to be meant are quite 

 distinct from the ordinary condition of that mass. These have excited the perplexed 

 observation of several geologists. They have been considered as intrusive and later 

 than the diabase, as transported blocks derived from a foreign source and as indigenous 

 in the rock in which they lie, while by Lawson they have been supposed to belong to 

 the Archean, on which the Keweenawan is supposed to rest. By the writer they 

 have always been considered a part of the Keweenawan, but how they acquired their 

 present forms and positions, and what their relations to the gabbro proper, have 

 been points which remained unsatisfactorily explained until quite recently. 



FIG. 2. DIAGRAM OF EXPOSURES FORMING THE TOP OF CARLTON PEAK. 



Mr. Elftman's observations of Carlton peak are conclusive to show that at that 

 place the feldspar masses were at first wholly surrounded by and now lie in and on 

 the Beaver Bay diabase. At the shore of Beaver bay the diabase is about and over the 

 feldspar masses. In the " pudding-stones " the feldspar masses are usually small 



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