Coiir/lomerate.s in Gneisslc Terranes. — A. WincheU. 257 
must be admitted, the reader may rationall}' infer that per- 
haps even Laurentian gneisses are also fragmental in origin. 
The evidence is that they ma^ 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 tei'ranes as in New England, for post-Laurentian 
terranes. 
If the gneisses of the Black Hills" 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 histor3^ 
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 comi^letely oblit- 
erated. 
I have cited the occurrence of pebbles in non-gneissic ter- 
ranes, as in Rhode Island, regardless of their age, because the 
-The allusion to the Black Hills was made only in the slip of 
■" Errata " attached to the " Extras " of my article. 
