PETROGRAPHIC GEOLOGY AND DESCRIPTIONS. 857 



Muscovadyt*.] 



fracture are so closely like the groundmass makes the porphyritic nature of the rock 

 very indistinct. 



Mic. The micro-gran ulitic groundmass is largely of quartz and feldspar. It 

 embraces much-altered crystals of feldspar, some biotite, apatite, Muscovite in large 

 masses and rarely a roundish quartz. One section. 



Age. Archean. 



Remark. This rock is allied to the granites and porphyries of Kekequabic lake. 

 Its relation to the granite of the region is not known. N. H. w. 



No. 2197. MUSCOVADYTE. 



S. W. J4 N. E. J4 sec. 4., T. 63-8, Disappointment lake, at Cheadle's cabin, site of an old iron exploration. 

 Ref. Annual Report, xxiv, page 62. Compare Nos. 1347, 1781, 1784, 1785 ; also Annual Report, xxi, pages 

 149, 150; Final Report, vol. iv, page 303. 



Meg. Fine-grained, gray, non-micaceous, mainly massiv^, but conglomeratic 

 in bands; firm, resembling muscovadyte. Position and dip like that of the conglom- 

 erate and tuff of the region. 



Mic. The most of this rock is made up of a fine-grained feldspar, which, 

 judged by several determinations on a bisectrix, varies from labradorite to andesine. 

 These fine feldspars are fresh and interlock in the manner of micro-gran ulyte. 

 Small hornblendes share in this groundmass and embrace the feldspars poikilitically, 

 but the largest poikilitic crystals are hypersthene. It is remarkable that a large 

 hypersthene crystal will maintain its orientation over so many of the feldspars, when 

 generally it makes less than one-half of the mass. Magnetite is distributed in fine 

 crystals. One section. 



Age. Archean (Keewatin modified). 



Remark. This rock shows the effect of the gabbro which lies but a short 

 distance further south on the basic Keewatin schist and conglomerate. There could 

 be no more ample and convincing proof of the origin of the rock which has been 

 called muscovadyte. It has been supposed to be a form of the gabbro, as it approx- 

 imates gabbro in composition and is nearly always near the gabbro margin. In the 

 field work it was very generally denominated muscovado, whether it had any 

 close association with gabbro or not. In the Twenty-first Annual Report a distinction 

 was made, as it was presumed that some muscovado was of irruptive and some of 

 metamorphic origin, and the name was assigned to a supposed phase of the gabbro. 

 It is, however, plain that here it is a product of metamorphisTn by the gabbro (or 

 cotemporary with it) on the Keewatin. N. H. w. 



No. 2198. MUSCOVADYTE. 



Same place as No. 2197. Same rock, but plainly conglomeratic. 

 Ref. Annual Report, xxiv, page 62. 



Meg. Fine-grained, pebbly portion of the same rock as No. 2197. 



