Gregory.] AEOOSTOOK LIMESTONES. 141 
flakes constitutes about five-sixths of the material present, and that 
quartz grains, with a little muscovite and other accessories, compose 
the remainder. 
Arenaceous sandstones of the same general character occur on the 
Aroostook River near the granite and along the railroad 2 miles east 
of Ashland Junction. 
AROOSTOOK LIMESTONES. 
This term is proposed for the thin-bedded, slated limestones which 
form the most widely distributed sedimentary rock type of this whole 
section of the North American continent. Its extent in northeast 
Maine is shown on the geologic map, and its yet more extensive dis- 
tribution in New Brunswick and Quebec is shown by an examination 
of the Canadian reports. The Aroostook River has cut its wide valley 
through this formation from Wade Township to its mouth, and has 
revealed the rock structure at many points along its course. The St. 
John River also flows over rocks of this series, and at the Grand Falls 
presents a good section for study of its lithologic character. In gen- 
eral, the limestone area is a low plateau about 500 feet above sea level, 
with a rolling surface made by rounded ridges between slowly running 
streams. The valleys are in general broad, and the whole region indi- 
cates an advanced stage of topographic development. 
Previous study. — The wide distribution of limestones has given this 
region rich agricultural land, which attracted settlers at an early date 
and gave the geologists the advantage of roads and cleared fields. 
The general monotonous character of the outcrops, however, gave 
little opportunity for special study. The members of the Jackson 
survey gave little information in regard to the series. Hitchcock 
briefly decribes the section from Houlton to Presque Isle, 1 and calls 
the rocks calcareous slates and limestones of Upper Silurian age. 2 
The most complete study of the slated limestones has been made by 
Professor Bailey, 3 who reviewed the work of previous writers and 
described the New Brunswick area in detail. He regards the follow- 
ing as the probable succession of strata, in descending order: 
Gray or greenish-gray (bluish weathering) argillites, with occasional alternating 
beds of greenish-gray sandstone. 
Gray, green, and bright-red slates, holding heavy beds of manganiferous hematite. 
Gray, highly calcareous slates, conspicuously banded on weathered surfaces, includ- 
ing at various points heavy beds of limestone, which are more or less fossiliferous. 
Gray, calcareous, and buff-weathering sandstones and slates, holding remains of 
crinoids, corals, brachiopods, and graptolites. 
Gray, calcareous conglomerates and sandstones, holding pebbles of Cambro-Sihn •inn 
rocks. 
1 Agriculture and Geology of Maine, 1861, p. 385. 
2 Geology of Northern New England, p. 3. 
a Ann. Rept. Geol. Nat. Hist. Survey Canada, 1885, l't. G, pp. 11-23. 
