210 BULLETIN OF THE 



thin section similar characters to No. 3, except that the feldspars are more de- 

 composed, and therefore less plagioclase could be seen, while the cj^uartz con- 

 tains more abundant trichites. 



No. 23. — A brownish red granite of similar composition with the preceding. 

 Feldspars colored pink and greenish white. Calcite and a greenish talcose 

 mineral occur as alteration products. In the thin section the feldspar is seen 

 to be greatly altered, and but very little of it shows any trace of triclinic 

 characters. The biotite is partly decomposed, and has a greenish color. The 

 general character of the rock is slightly more basic than the two preceding, 

 but we do not consider that there is enough difference to lead us to regard 

 them as distinct. We should rather regard them as parts of the same forma- 

 tion. 



No. 25. — In this specimen the greenish feldspar predominates over the 

 pink. The rock shows abundant signs of weathering, containing numerous 

 cavities formed by the decomposition of its ferruginous minerals, and now 

 partially fdled with hydrous oxide of iron. Under the microscope this is seen 

 to be the most decomposed of any of the specimens, the biotite being almost 

 whoUy changed, and almost no plagioclase being recognizable. Many parts of 

 the rock are filled with viridite. The quartz, besides its numerous fluid inclu- 

 sions, contains dodecahedral quartz crystals of the same character as those so 

 commonly seen in the quartz of rhyolite. This rock is similar to No. 23. We 

 should regard these rocks as eruptive, but we are well aware that others would 

 claim that the microscopic characters are those which belong to metamorphosed 

 sedimentary rocks. 



No. 57. — This rock is seen in the hand specimen to be composed of flosh- 

 red orthoclase, pale greeidsh white feldspar, somewhat decomposed, together 

 with altered biotite and quartz. The biotite has been changed to a chloritic 

 material. The minerals give to the rock a greenish red color. It is more 

 coarsely crystalline than the other specimens from Mt. Ktaadn, and in its 

 general facies is somewhat unlike specimens 3, 5, and 25. 



The lower two thirds of the basin walls are composed of the gray 

 granite, which is similar in composition and appearance to that of the 

 lower slopes of the mountain on the south side, and to that of Katep- 

 skonegan Falls, except that the rock of the localities last indicated con- 

 tains only the white feldspar. The upper third of the walls consists 

 chiefly of the red variety (5), the modifications represented by Nos. 23, 

 25, and 57 being found only upon the very highest parts of the moun- 

 tain, — the East and West peaks, the serrated crest, and the ridges that 

 connect those portions. The rock represented by the last three num- 

 bers is throughout so badly decomposed that only once was a sfjecimcn 

 (57) obtained tolerably sound and firm under the hammer. The rock 

 represented by No. 5 is oftenest, but not always, found in a crumbling 



