78 The Aiuericdn Gcologi.st. August, 1895. 
sandstones and marls are later instead of earlier than the bulk 
of the great Keweenawan traps. However, regardless of these, 
it may be shown that the lowest part of the Keweenawan, as 
described by Irving, and later by the Minnesota survey and 
by Prof. Van Hise, consists of massive sandstones and con- 
glomerates. Reference may here be made to the composition 
of Grand Portage island, in the northeastern part of Minne- 
sota.* At this place is a white sandstone and a conglomerate 
which show unmistakably that the Keweenawan is separated 
from the Animikie by an important erosion interval. Below 
this interval is the upheaved and metamorphosed Animikie, 
the same that has l)een examined on Pigeon point by Bayley.f 
Pebbles from this changed Animikie and from the attendant 
eruptives (quartz-porphyry and felsyte) are in this conglom- 
erate mingled with pieces of Animikie slate. Over the con- 
glomerate is a white siliceovis sandstone. This conglomerate 
seems to extend for some distance below the water level, since 
pieces of it having somewhat different characters are on the 
beach of the island. It has been seen also at other places. A 
recent re-examination of the valley of the St. Louis river, be- 
low Carlton, reveals the existence of remarkable diiferences in 
the fragmental conglomerate which there lies on the Archean 
slates (Keewatin). The lowest portion is a purely quartzose 
though strongly pyritiferous conglomerate, with pebbles 
which sometimes are several inches in diameter, becoming 
gray sandstone above.;]; The materials of this conglomerate are 
referable wholly to the rocks of the pre-Keweenawan. Careful 
search did not bring to light a single Keweenawan pebble, al- 
though the gabbro hills rise in the immediate vicinity to the 
hight of over 500 feet. Its structural features indicate a 
greater age than that of the overlying conglomerate. A finer 
red conglomerate and red sandstone and shale lie upon the 
gray conglomerate, and are charged with pieces that can only 
be referred to the rocks of the Keweenawan iminediately adja- 
*U. S. Grant, Note on the Keweenawan rocks of Grand Portage is- 
land. American Geologist, June, 1894, vol. xiii, p. 437. 
See also earlier references to this basal conglomerate by the writer, 
viz., 16th Minnesota report, pp. 55-56; 18th ditto, pp. 42-43. 
tThe eruptive and sedimentary rocks on Pigeon point, Minnesota, 
and their contact phenomena. Bulletin 109, U. S. Geol. Sur. 
JTenth Minnesota report, p. 33, 1881. Twenty-third ditto, p. 239. 
1895. 
