38 THE GEOLOGY OP MINNESOTA. 



[The Kekequabic granite. 



similar conversion of all finer feldspathic debris into a fine interlocking back- 

 ground. 



2. Sometimes biotite occurs at this stage, but is more likely to be abundant 

 under powerful metamorphosing action. 



3. Epidote permeates the old feldspars and gathers independently. 



4. Quartz and feldspar. Sometimes one and sometimes the other is plainly 

 earlier, but usually they were about contemporary as to date of origin. 



Therefore, in conclusion, there is reason, as has been shown also in several of 

 the annual reports, for classing this rock, from the point of view of its intrusive 

 action and crystalline texture, with the granites, and at the same time there is much 

 evidence, from another point of view, both structural and petrographic, for classing 

 it amongst the elastics metamorphosed- by some force which has acted at least 

 throughout the area of Kekequabic lake. 



It is also reasonable to conclude that as an intrusive rock it is derived from the 

 clastic beds in xilx, and had no deep-seated source. As an intrusive it was at least 

 plastic, probably rendered so by a combination of heat and moisture, and was probably 

 at the same time under great pressure. 



The action of aqueo-igneous fusion has recently been investigated by Crosby 

 and Fuller,* and has been recognized by numerous geologists as an efficient cause in 

 rendering plastic and even fluid the sedimentary materials when subjected to 

 sufficient heat, moisture and pressure. When in that state the sedimentary materials 

 would not only be recrystallized thoroughly but would act the part of intrusives on 

 the strata adjacent or superjacent and they would necessarily exhibit the same 

 chemical variations, within broad extremes, as the sedimentary strata themselves. 

 This action of the elastics under pressure is well exhibited in the limestones of the 

 Adirondacks, which according to numerous observers have been made to intrude the 

 adjoining quartzytes and gneisses, and to surround isolated portions of them much in 

 the same manner as igneous rocks. This fact led Emmons and some of the early 

 geologists to class crystalline limestone amongst the igneous rocks. But this action 

 is mutual isolated pieces of limestone are included in the adjoining gneiss, indi- 

 cating a common history and hence a similar origin. 



If this source of the granitic rocks be admitted in the case of the Kekequabic 

 lake granites, it is likely to have been equally efficient in other localities, and indeed 

 it rises to the importance of a general cause, applicable, in the absence of other suffi- 

 cient source, to all the granites of the state. Indeed the same facts, leading to the 

 same conclusion, are observable at other places, and especially about Snowbank lake. 

 The Kekequabic Lake granite, however, is a small isolated area, and the transitions 



Origin of Pegmatyte. American OeolwjM, vol. six, 1897, pp. 147-18U. 



