THE IGNEOUS EOCKS. 505 



whicli iire other lighter areas eoniposed of quartz, saussurite, ealcite, and 

 large irregular cellular garnets. 



A singular set of knobs is north of Lake Corning, in the SW. 4 sec. 5, 

 T. 47 N., R. 27 W. (Atlas Sheet XXV). The main mass of these knobs is a 

 coarse-grained nralitic diabase resembling a camptonite, with lath-shaped 

 feldspars and hornljlende crystals scattered through a fine-grained, grayish- 

 green matrix (Specimen 19547). On the top of the hill the rock is coarser, 

 and its feldspathic constituent is in patches and is of a pinkish tinge (Specimen 

 19548). The hornblende is in acicular crystals. Farther east the feldspar 

 crystals are larger and redder, while the hornblendes are not acicular 

 (Specimen 19549). Certain patches in the rock were taken for inclusions. 

 They are pink in color and are very much finer in textui'e than the main 

 mass of the rock, and around their edges they are bord(n-ed by bands of 

 green, as though they had been affected by contact action. Other patches 

 ai"e epidotized throughout. In both cases the "inclusions" resemble fine- 

 grained granites that have been altered by the greenstone. 



In thin section the main mass of rock is seen to have a coarse diabasic 

 structure. The hornblende is always found in ophitic areas, either alone 

 or with chloi'ite and epidote. The plagioclase is changed to a mixture of 

 saussurite, ealcite, and epidote, which is cut through and through by horn- 

 blende spicules. The rock is thus a uralitic diabase, like so many others 

 of the knob greenstones, and not a camptonite, as it appears to.be from its 

 macroscopic habit. 



The porphyritic phases on the top of the hill (Specimen 19549) are 

 composed of larg-e, partially idiomorphic, altered, and often crushed ;ind 

 reddened plagioclases in a matrix of small laths of the same mineral 

 and small triangular masses of chlorite that have evidently been derived 

 from hornblende. Leucoxene is also })resent in large quantity. The 

 supposed inclusions are fine-grained diabases. They contain only small 

 quantities of the chloritic interstitial substance, wdiile large quantities of 

 ealcite and leucoxene are present in them. The epidotized inclusions are 

 of the same nature, except that they contain an abundance of epidote. 



The "inclusions" may be fragments of a preexisting, fine-grained dia- 

 base, caught up by the coarse diabase in its upward passage, or tliev may 



