200 Conglomerates in Oneiss'u: Terranes. — A. Winc/iell. 
Avoald generall}' be admitted. It is surprising, as may be re- 
marked in passing, that the nature of the associated beds has 
not been claimed as evidence of a general aqueous history of 
the whole Laurentian. But as long as the gneisses were free 
from pebbles and conglomerates the evidence of their aqueous 
origin was rather presumptive than direct. On the contrary, 
the cases which it was the main purpose of my paper to de- 
scribe, presented pebbles in the midst ofgneissic masses, and 
a conglomerate imhedded comjiletelg in a gneiss so massive 
as to have been commonly denominated a syenite. The mat- 
rix itself is a characteristic gneiss. I am not aware that such 
occurrences are "well known." 
The conglomerates cited by Logan have lithologie associ- 
ations quite analogous with those of the so-called Huronian 
conglomerates. The associations are directl}^ with sediment- 
ary rocks, more remotely with crystalline rocks. It was not 
my purpose to refer to conglomerates so situated — any fur- 
ther than to quote the passage from Credner in which the ag- 
gregate mass of conglomerates in the Archaean is mentioned. 
In the general discussion of conglomeritic occurrences in 
terranes more or less crystalline, references should be made 
to the observations of professor W. O. Crosby.^ 
The nucleus of the Black Hills has been again and again re- 
ported granitic. But Crosby states that granites occur only as 
lenticular masses conformable with the stratification of the 
schistose rocks. This, in fact, was previously reported by N. 
H. Winchell and by Newton. In the eastern or newer series 
of Arch;ean rocks, occurs an important quartzite which, in 
places, "passes into coarse grits and conglomerate," the peb- 
bles of which have sufliered extensive deformation. Professor 
Crosby reg;ifds the conglomerate and associated schists as 
"strikingly similar to the metamorphic sediments occurring at 
I'x'Uingham, Massachusetts."'' "It is perfectl}^ plain," he 
^:lys, '"that the metamorphic series consisted originally of in- 
terstratified beds of ordinary mechanical sediments — slate, 
sandstone and conglomerate ; and the metamorphic agents 
have not only accomplished the chemical change implied in 
the fact that these rocks are now in the main, distinctly hydro- 
* Geoloqy of the Black Hills of Dakota. From the Proceedings of the 
Boston Society of Natural History, Vol. XXIII, pp. 488-517. 
'" Proc. P.oston Soc. Nat. Hist., XX, 373-8. 
