1886.] NATURAL SCIENCES OP PHILADELPHIA. 19 



THE INCLUSIONS IN THE GRANITE OF CRAFTSBURY, VT. 



BY CALVIN Mccormick. 



The inclusions usually found in granites are observed to vary 

 to a marked extent in outline, structure and mode of occurrence. 

 Yery often they resemble imbedded fragments of older rocks. 

 They are usually darker than the including granite, and are either 

 circular or angular. When rounded they resemble an enclosed 

 pebble ; when angular, a fragment of slate or mica schist. They 

 sometimes merge into the surrounding rock by thrusting out 

 minute connective particles. They are generally finer in texture, 

 and hence less easily decomposed by atmospheric agencies than 

 the enclosing granite. 



A reference to the recorded observations on granitic inclusions 

 will doubtless assist materially in the study of the subject. In 

 1821, Dr. John Macculloch, in his "Geological Classification of 

 Rocks," p. 230, refers to inclusions as "irregular patches or veins 

 of a fine texture, spheroidal in arrangement, imbedded in coarse 

 granite." In 1858, Dr. Cavl F. Naumann refers to "pseudo-frag- 

 mentary concretions resembling sharp-angled fragments common 

 in crystalline siliceous rocks." (Lehrbuch der Geognosie, 2 Auf., 

 Band I, S. 422, 560; B. II, S. 203.) 



In the same year Dr. F. Hochstetter states that " the granites 

 of Billston Island contain micaceous fine-grained, dark, globular 

 enclosures." ( Jahrb. k. k. geolog. Reichsan., S. 285.) 



In 1863, Dr. F. V. Andrian, referring to the hornblendic granites 

 of Central Bohemia, mentions " innumerable fine-grained enclos- 

 ures, sharply segi'egated from the surrounding rock, varying in 

 size from -^^ to 4 inches in diameter. These enclosures contain 

 small quantities of hornblende crystals. From their abundance 

 and identity of constituents they were produced during the solidi- 

 fication of the rock mass, by a process of segregation, the exact 

 nature of which is unknown." (Beit. z. Geolog. d. Kaur. Tab. 

 Krei. Bohmen, S. 166.) 



In an article on the " Metamorphic Origin of certain Granitoid 

 Rocks and Granites in the Southern Uplands of Scotland," Prof. 

 James Geikie describes " nests of altered rock in a gray granite. 

 These are distinctly laminated, fine-grained, micaceous and 

 imparting a dark shade to the rock. They are irregular in shape, 



