igneous Ejections 46? 



rocks described in bulletin number 150 of the United States Geological 

 Survey. It comes from another area, but both rocks are the same in 

 composition and appearance. The epidote is common, but not universal. 

 The Bethlehem area extends easterly into Whitefield and Jefferson, and 

 is very commonly foliated. It narrows to a point in North Lisbon, and 

 seems to have cut off the northeastern extension of the Paleozoic strata 

 of the Ammonoosuc district. The foliated planes have an average dip 

 of about 70 degrees north 30 degrees west. Were it not for abundant 

 inclusions of mica schist, one would be inclined to retain the old name 

 of gneiss or schist for the group. The fragments are particularly abundant 

 in the western part of the area, which, as will be seen readily on the 

 geological map, plate 43, is to a certain extent coterminous with the 

 apparent place of the schists that have been absorbed by the igneous 

 intrusions. Portions of the mass may be the original slate thoroughly 

 interpenetrated by an igneous paste, but it has been so changed that it 

 more closely resembles the granite than the original strata. 



Hornblende Rocks 



These do not cover large areas, but are quite common, and of too 

 small extent to be represented on the map. The most important is on 

 the Ammonoosuc, above the village of Lisbon, following up the Oregon 

 road toward the argillite. Smaller patches are common in the Lisbon- 

 Swift water complex, and supposed to be of igneous origin. There are 

 besides many crystalline schists containing hornblende or actinolite 

 needles of secondary origin. 



A sample of a dike cutting and altering the slates at North Lisbon 

 was submitted to Mr W. C. Phalen, who reports as follows : 



"Number 2. — This rock has a schistose structure, and there is evidence of its 

 schistose nature even in the thin-section that has been studied. Hornblende 

 needles in abundance, brown mica, magnetite, quartz, and feldspar constitute the 

 major portion of the rock, which might appropriately be termed an amphibole 

 schist." 



This report is of value because, in connection with the observed phe- 

 nomena, it seems to be proved that the hornblende schists of this district 

 are of truly eruptive origin, and that the date of their ejection is posterior 

 in time to the age of the slate. The hornblende schist seems to be allied 

 to diorite rather than to diabase. 



Contact Phenomena — Lyman Schist 



Quite a large class of rocks have been affected by these igneous in- 

 trusions, which were not well understood at first, for the study of the 



