Conglomerates in Gneissie Terranes. — A. Winchell . 257 
must be admitted, the reader may rationally infer that per¬ 
haps even Laurentian gneisses are also fragmental in origin. 
The evidence is that they may be fragmental. When there¬ 
fore, in addition to this presumption, I cite similar conglom¬ 
erates from the recognized Laurentian of Canada and Minne¬ 
sota, we have the same evidence for a fragmental origin of 
Laurentian terranes as in New England, for post-Laurentian 
terranes. 
If the gneisses of the Black Hills 2 are also post-Laurentian 
the fact of the association of pebbles and conglomerates has 
the same significance as the facts cited from New England— 
neither more nor less. 
As to the case of included fragments which evidently are 
not water-worn, mention is made of them only to prove the 
contemporaneousness of the gneiss mentioned with processes 
of sedimentary rock-making. If such contemporaneity exist¬ 
ed in New England gneisses, it may presumably have existed 
with Laurentian gneisses; and when I cite hundreds of simi¬ 
lar fragments in Laurentian gneisses, the evidence rises from 
analogy to demonstration. Gneiss-making and sediment¬ 
forming could not be coincident in time and place, if gneiss 
originated from igneous fusion and sediments accumulated 
from watery immersion. But no one doubts that sediments so 
originated; gneisses associated with them, therefore, must 
have had an aqueous history. 
As to New England granites of such character or collocation 
with schists as to show, as at Mount Pequawket, that they 
have been in a state of fusion, there is neither reason to doubt 
the evidence nor to be misled by it. If granites generally 
have resulted from metamorphism of sediments, it is ex¬ 
tremely probable that, exceptionally, the metamorphism 
reached the stage of fusion, accompanied as it almost neces¬ 
sarily would be, by eruption and vein-filling. Many granite 
veins, nevertheless-, may have originated from heated solu¬ 
tions, and others from in-squeezed plastic material in which 
the planes of sedimentation had not become completely oblit¬ 
erated. 
I have cited the occurrence of pebbles in non-gneissic ter¬ 
ranes, as in Rhode Island, regardless of their age, because the 
2 The allusion to the Black Hills was made only in the slip of 
“ Errata ” attached to the “ Extras ” of my article. 
