172 CONTRIBUTIONS TO THE GEOLOGY OF MAINE. [bull. 165, 
I. Andcsite, Edmunds Hill, Aroostook County, Maine. Analysis by W. F. Hillebrand. 
II. Hornblende-andesite, Mount Shasta, California. Analysis by H. N. Stokes, Bull, U. S. Geol. Sur- 
vey No. 148, 1897, p. 190. 
III. Hornblende-dacite, Anzeion,iEgina. Analysis by Dr. A. Rohrig. H. S.Washington, Jour. Geol., 
Vol. Ill, p. 150. 
IV. Pyroxene-andesite, Pefion de Pitayo, United States of Colombia. Kuch, Geol. Studien in der 
Republik Colombia, Pt. I, Berlin, 1892. 
V. Pyroxene-andesite, Agate Creek, Yellowstone National Park. Analysis by Whitfield, Bull. U. S. 
Geol. Survey No. 148, 1897, p. 134. 
VI. Hypersthene-andesite, Crater Peak (Lassen Peak region). Analysis by W. F. Hillebrand, Bull. 
U. S. Geol. Survey No. 148, 1897, p. 197. 
VII. ? Andesite, Fox Islands, Maine. Analyses by E. W. Magruder and W. A. Jones, in Johns Hopkins 
University Laboratory. G. O. Smith, Geology of Fox Islands, Maine. Presented as a thesis, 
Johns Hopkins University, 1896. 
From a study of the above tables it becomes apparent that the 
Edmunds Hill rock presents no points of distinction from recognized 
types found elsewhere, and the tables could be greatly enlarged by 
the ^addition of closely similar analyses. The analysis in Column VII 
requires some notice. The rock is described as a red andesite, with 
"rather basic" feldspars and with calcite and magnetite present. 
The altered condition of the rock made accurate optical determination 
impossible. In discussing the analysis the writer says: 1 "In its 
mineralogical composition this rock approaches the basaltic type, but, 
as the analysis shows, is somewhat too acid. The olivine phenocrysts, 
moreover, are not very numerous, and there is reason to regard this 
as simply an olivine-bearing phase of the andesite." The description 
is of an andesite, but there are discrepancies between the description 
and the analysis. No ferrous iron is present to form magnetite, and 
if the small amount of lime forms calcite basic feldspars could not be 
produced, and even if the whole 0.59 per cent of lime were present as 
andesine or labradorite the amount is far too small for an andesite. 
According to the generally accepted usage among petrographers, a 
rock with so high a percentage of soda and potash, with little lime 
and magnesia, would be classed as a trachyte, or, more closely, an 
segirine-trachyte. 
HORNBLENDE-ANDESITE. 
The largest single mass of this rock is Hobart Hill, and the freshest 
and most typical specimens are from this hill and from the west bank 
of the Presque Isle near the northeast foot of the hill, where quarrying 
was at one time attempted. The hand specimen shows a very dark- 
gray, almost black, rock, fine-grained, but with a somewhat porphyritic 
appearance, caused by the occasional feldspar crystals which rise above 
the general groundmass and reflect light well from their glassy cleavage 
faces. Some few feldspar laths attain a length of 5 to 6 millimeters. 
The rock breaks out into tabular blocks along the cleavages and weath- 
ers to a brownish-gray color. 
Microscopic description. — In thin section the microscope reveals 
magnetite, apatite, titanite, occasionally a zircon lath, possibly augite, 
Geology of Fox Islands, Maine, p. 34. 
