144 THE GEOLOGY OF MINNESOTA. 



| Crystalline rocks. 



ance of the plug-and-feather in reducing the large blocks to sizable and 

 desired dimensions. 



The composition of the red syenite from East St. Cloud (No 6) is not 

 very different from the foregoing, but the feldspar is mainly flesh-red, and 

 all the grains are coarser. It also has a higher percentage of silica, a fact 

 that has been discovered practically by the owners who have given up the 

 general use of it because of its being more costly to work. In some of the 

 outcrops west of St. Cloud, in Stearns county, it becomes coarser-grained, 

 somewhat resembling the red Scotch granites imported to the United States. 

 In the winter of 1874-5 a block weighing ten tons was taken out of the red 

 granite quarry about three miles west of St. Cloud for a monument base. 

 It was polished at St. Cloud and was delivered to its purchaser at Chicago. 

 This was very fine and greatly resembled the Scotch granite in color, grain 

 and polish. At the point where this was taken out the granite rises about 

 twenty feet above the general surface, and spreads over more than an acre. 

 A similar red granite, found at Watab (No. 10), has furnished several hand- 

 some monuments, some of which were put on exhibition at the Centennial 

 Exposition of 1876, at Philadelphia, by Mr. Gurney, the owner. 



The other gray granite (No. 7) which is found at the East St. Cloud 

 quarries has been noticed at several other places, and it is probably largely 

 distributed wherever the red granites are found. In some places it passes 

 by a gradual change into the red, in such a way as to suggest that the 

 whole was originally gray, and that the red color has been superinduced 

 since its formation by some difference of exposure to the elements. It is 

 No. 835 of the geological survey series.* The true composition of this 

 rock is not readily ascertained by simple ocular inspection, since the 

 quartz and the feldspar are very similar in color and luster. When freshly 

 quarried they both appear glassy ; the cleavage of the feldspar is not evi- 

 dent, though that mineral exhibits an irregular parting or stepstone frac- 

 ture, and when in compact mass it seems to be translucent. Hence the 

 general aspect is very much like that of the gabbro of Duluth when freshly 

 quarried. It has a clear, bluish-gray, uniform color, and is feebly trans- 

 lucent. The whole content of silica in this rock is 74.72 per cent., being a 



Tenth annual report, p. HI. 



