Basic Eruptive Hocks. — Merrill. 53 
tions (28519) it shows a dense irresolvable base, the true nature of 
which is badl}' obscured by calcite and ferruginous decomposition 
products, but which was once evidently a glass. Throughout 
this base are thickl}' scattered al)undant acicular plagioclases, iron 
ores in granular and gratelike forms and occasional larger rounded 
blebs of more or less serpentinized olivines. Hornblendes or 
augites if ever existing, have been obliterated by decomposition. 
This rock yielded Prof. Packard 39.40% Si 0,. No other dikes, 
of which this might be considered an offshoot, were discovered in 
the vicinity. 
Going still farther south two small dikes, one 15 inches and one 
3 feet wide, were fov^nd exposed in the railroad cutting of the 
Lewiston and Auburn railroad on the west liank of the Little 
Androscoggin river nearly opposite the Barker cotton mill. 
(Locality (5) on map). These show a structure in every way 
identical with those first descrilied south of the Androscoggin 
mill and from their position (nearly due west) there seem good 
reasons for assuming them to be a continuation of the Cedar 
street dike in Lewiston. A complete analysis of one of these 
rocks (28531) is given on p. 54. In a cutting of the Maine Cen- 
tral railroad, south of the Ta3'lor Brook crossing, and about a 
mile below the city of Auburn occurs still another dike about 12 
inches in width (locality (6) on map). This rock (28532) in 
the thin section is indistinguishable fromHawes, dike 1, (diabase) 
at Campton Falls, New Hampshire.* It yielded Prof. Packard 
39.46% Si Og and is presumably a continuation of the dikes 
south of the Androscoggin mill on the Lewiston side of the river. 
Farther to the west, between the well known tourmaline and 
lepidolite locality, fancifully known as "Mount Tourmaline" and 
Stevens mill, is another dike five feet in diameter (28658) which 
shows also a camptonite structure and composition. It is to be 
noted, however, that slides in the Museum collection from other 
dikes having the same trend, but l3'ing to the northwest, near 
Ta^'lor pond, are normal diabases and ophitic in structure. 
The next dike met with, traveling south along the M.C. R. R., 
is found just before reaching Danville junction. This is a large 
dike of normal olivine diabase (35056) which yields some 46% 
SUV 
*Dr. Hawes' original specimens and thin sections are in possession of 
this department. 
