256 Conglomerates in Gneissie Terranes — A. Winehell. 
■cited many instances- of fragments of schists and other pre¬ 
existing rocks included in it, many of them showing signs of 
alteration. There is nothing about any of these fragments to 
suggest attrition. Furthermore, all our true eruptive granites 
are post-Laurentian, if not of paleozoic age. This is certainly 
true of the majority of examples, and those the ones most 
typical. At all events, granting the rounding of fragments, 
the work of remodelling was effected in paleozoic times, and 
hence is not Laurentian. 
Furthermore, as to the cases you cite from Minnesota, the 
pebbles are of rocks recognizable as Laurentian. Hence one 
of two conclusions should follow. Either the pebbles came 
from a pre-Laurentian terrane, or the conglomerate being 
made of Laurentian materials is post-Laurentian. Both con¬ 
clusions ^re opposed to the sentiment of your paper. If there 
is any metamorphism of a conglomerate in the Saganaga- 
pebbles, I should judge from your description, it is the Ogishke 
Conglomerate that has been affected, which is only 15 miles 
distant and “stocked with similar pebbles.” 
CONGLOMERATES ENCLOSED IN GNEISSIC TERRANES. 
[Supplement;] , 
By Alexander Winch ell. 
My article on the subject above named has elicited many 
comments, some of which render it desirable to supplement 
the article with explanations and new evidences. One es¬ 
teemed correspondent whose familiarity with New England 
geology is everywhere recognized, reminds us that the ter¬ 
ranes from which boulders and conglomerates have been cited 
in Vermont, Massachusetts and Rhode Island, are post-Lau¬ 
rentian. 1 This was well understood in making the citations.. 
They were not made for the purpose of proving directly the 
fragmental origin of Laurentian gneisses. Some of them 
were intended to remind geologists that certain terranes gen¬ 
erally recognized as real crystalline gneisses—however dis¬ 
tinguishable from Laurentian gneisses in position or petrog¬ 
raphy—inclose features incompatible with an eruptive origin. 
If, however, an obviously fragmental origin of any gneisses 
1 See the communication from Professor C. H. Hitchcock in the 
present number of the Geologist. 
