go NEW YORK STATE MUSEUM 



unique inclusion of light greenish pyroxene rock (^altered limestone) 

 is found inclosed in the granite just inside the border zone of 

 garnet gneiss, six-tenths of a mile east of Pyrites. The restriction of 

 such nonamphibolitic material to the margins of granite bodies 

 would suggest the view that the Grenville xenoliths which were 

 carried farther into the interior of the magma were uniformly 

 changed to amphibohte, that the failure of inclusions at the margin 

 of the igneous masses to be similariy aflPected is merely due to the 

 interruption of the process of alteration through solidification of the 

 magma. 



WTien, however, the evidence ;f the detached individual frag- 

 ments of garnet gneiss is more closely studied, it fails to lend con- 

 vincing support to this interpretation. In these xenoliths, as also 

 in the pyroxene rock above cited, there is a total lack of marginal 

 gradation, abrupt or gradual, to an amphibolitic alteration product, 

 and accordingly this type of transformation can not be said to have 

 been going on at these points when the sohdification of the magma 

 occurred S::::r. therefore, it is impossible to detect the progress 

 of the al:rr: : in the neighborhood of the border of the magmatic 

 chamber, v.er: a more rapid cooling of the intrusive must have 

 tended to preserve the different stages :: the process, it is likewise 

 impossible to assert definitely that it has taken place in the interior. 

 In the central part of the granite bodies, indeed, there is a total lack 

 of xenoliths which show transition from a t\-pical Gren\-ille aspect 

 to an amphibolitic product, and this fact, together with the con- 

 siderations noted above, favors the view that few fragments of 

 limestone or biotite schist or other Gren\-ille t>-pe, except garnet 

 gneiss, were included as such within the granite magma, that all 

 had ur.^rTcne at or near the margin of the intrusive body, what- 

 ever :-.:::^e5 the magma was capable of producing upon them 

 and that where engulfed, the majority- of such inclusions, whatever 

 may have been their original character, had already been altered 

 to amphibolite. 



In A-iew therefore of the great abundance of homblendic inclu- 

 sions in the granite areas, and the apparent inability- of granite con- 

 tact alteration alone to account for such i v?.?t quantit\" of this 

 material, i: ha? seemed necessar}- :: see!: r::ative or supple- 



mentar}- source, quantitatively ' e ' the problem. 



In the writer's opinion this is : : i : ^ ? and related 



amphibolite schists which were intruded and in great measure 

 metamorphosed prior to the introduction of the granite. With a 



