1886.] NATURAL SCIENCES OF PHILADELPHIA. 23 



The Relation of the Nodule to the Rock Mass. The line of 

 contact between the inclusion and the including rock is not always 

 distinct. But it is possible to extract the former with compara- 

 tive ease. The remaining cavity, however, is usually lined with 

 biotite, which, adhering to it rather than to the nodule, indicates 

 that the inclusion was originally formed from the rock mass. 

 Sections across this line of contact, show considerable quartz and 

 a small quantity of biotite. These minerals are apparently inter- 

 locked, further denoting that the biotitic mass belongs to the 

 surrounding rock. 



General Conclusions. First, concerning the nodules : These 

 are not micaceous rolls, for their structure internally shows dis- 

 tinct bands. ^ or are they concretions, for no nucleus is observed. 

 But they are masses of flakes of biotite cemented with quartz, 

 abnormally segregated from the original granitic mass. These 

 flakes, although originally concentric, were afterwards arranged 

 radially, hence producing the nodular form. (Dr. Zepharowich, 

 Mineralogical Lexicon, Austria, p. 59.) 



Second, concerning the granite : The presence of these nodules 

 indicates the igneous origin of the granite. Were the original 

 mass in aqueous solution, the material would have been evenly 

 distributed, and the nodules could not have occurred. Were it 

 of metamorphic origin, the nodules would scarcely be so uniform 

 in outline and microscopic appearance, but would be more or less 

 contorted. These nodules denote a state of fluidity of the entire 

 mass which resulted from igneous agencies. While in this fluid 

 condition, the nodules first formed, and were enclosed by the 

 surrounding mass. This is sustained by the wrinkled and folded 

 surface of the nodules, which doubtless was occasioned by the 

 contraction of the surrounding mass as it cooled. 



The fact that biotite is a frequent constituent of igneous rocks, 

 has its influence in sustaining the igneous origin of this granite. 

 This is also sustained by the investigations of local phenomena. 

 (Geology New Hamp., vol. 1, p. 538.) 



The inclusions at Craftsbury are unique in type, diff'ering from 

 those of all other localities. 



These observations ma}' be modified by further investigations, 

 but it is hoped that they maj'^ elicit an extended interest in the 

 subject. 



Appendix. Since the preceding pages were written, my atten- 



