A CONTRIBUTION TO THE GEOLOGY OF SOUTHERN MAINE 545 



Norm and Mode. — The correspondence between norm and 

 mode is not close. The lime is not in anorthite, but in ferro- 

 magnesian minerals, mainly hornblende. The alumina is not 

 all in feldspar, but also in hornblende giving an alferric mode. 

 Diopside, hypersthene and ilmenite are lacking. The titanium 

 is in titanite. The normative amounts of quartz, orthoclase, 

 albite and magnetite are present. 



Microscopic Character. — Green hornblende is found to be the 

 prevailing mineral. It is arranged in parallel leaves, giving the 

 schistose structure. The schistosity is not perfect, but is in- 

 terrupted by many crumpled areas and by occasional patches 

 where the minerals are without orientation. The texture 

 simulates the granitic. Titanite is abundant. Plagioclase 

 (albite and oligoclase) is moderately abundant, with a little 

 orthoclase and less quartz. There is found to be no great 

 mineral ogical difference between the gray and the black types. 

 The gray have been more intensely crushed and the light bands 

 are due to granulated quartz and feldspars. These are present in 

 the black variety also but are less crushed and so do not appear 

 white in the hand specimen. There is a slight kaolinization of 

 the feldspar. The orthoclase has inclusions of the reddish 

 black dust mentioned before. Small amounts of apatite and 

 magnetite are present. 



Comparison with Monhegan Rocks. — The close analogy of this 

 rock with those from Monhegan Island described by Lord 1 

 which fall into the same subrang is so striking that his analyses 

 are reproduced for comparison together with ours. Since some 

 of our later dikes also fall into this subrang, the discussion will 

 be taken up after they have been described. The comparative 

 table of analyses will be found on page 554. 



The most conspicuous difference between the Monhegan rocks 

 and the schist of the mainland is that the former contains 

 olivine in both norm and mode, while the hornblende schist 

 does not. Moreover there is a slight excess of silica in the 

 schist, while two of the Monhegan rocks lack silica to the 

 extent of having nepheline in the norm. 



4 Am. Geol., XXVI, pp. 340 and 346. 



