384 The American Geologist. June, 1393 
never been carefully studied microscopically and chemically. It 
is found in two facies, a granitic and a porphyritic, which seem 
to be rather distinct from each other in their field relations and in 
hand specimens, but in reality they are very closely related, un- 
doubtedly forming parts of the same rock mass. The granitic 
facies occurs in a roughh' oval area whose major axis (east and 
west) is about four miles, the minor axis being less than two. It 
has been descril)ed as a fine s^^enitic gneiss or granite* and as a 
pyroxene granite, t The porphj-ritic facies is confined to a number 
of small, isolated areas occurring irregularl}- in the clastic rocks. 
The minerals composing the granite are feldspar (mostly anor- 
thoclase), quartz and augite, with accessor}' hornblende, biotite, 
apatite and sphene. The structure of the rock is truly granitic, 
its description as a gneiss arising from the fact that it is some- 
times broken into roughly parallel layers, but there are no 
structural or mineralogical diflferences between the layers. The 
granitic facies is of a dull pinkish color and of medium grain; 
the feldspar often shows a decided tendency to a more or less 
complete idiomorphic development. The prophyritic facies is 
of a gray color and has a very fine-grained — almost microgranitic 
— crround-mass composed of quartz and feldspar; in this ground- 
mass are imbedded numerous large and sharply outlined phen- 
ocrysts of feldspar and smaller ones of augite. The feldspar 
phenocrj'sts are sometimes arranged in roughly parallel lines, but 
this is never very pronounced. 
On chemical analysis the two facies are found to agree very 
closely. A noticeable fact brought out by these analyses is that 
in l)Oth cases the proportion of soda is very much larger than 
that of potash. Using the term "soda-granite" as a true granite 
in which the soda is in excess of the potash, this rock would 
belong to the series of soda-granites, which, while reported from 
several localities in Europe, have as yet been rareh' found in 
America. Such a rock has been described by W. S. Bayley from 
Pigeon point, Minnesota, on the north shore of lake Superior, 
in connection with a quartz-keratophyre. + The analyses of both 
*N. H. Winchell, Geol. and Nat. Hist. Survey of Minn., 15th (1886) 
Ann. Rep., pp. 3(11-36!); 16th (1887) Ann. Rep., pp. 100-108. A. Winchell, 
Ibid., 15th Ann. Rep., pp. 149-156. 
fU. S. Grant, Ibid., 20th (1891) Ann. Rep., pp. 69-82. 
t A quartz-keratophyre from Pigeon Point and Irving's augite-syenites. 
Amer. Jour. Sci., (3) vol. 37, pp. 54-62, Jan., 1889. 
