has 
HISTORY OF CRYSTALLINE ROCKS. 33 
§ 59. These various endogenous deposits are instructive illustrations of the crenitic 
process. The alternations of stratiform layers of quartz, of calcite, and of feldspathic and 
pyroxenic aggregates, with included layers of apatite, pyrite, etc., show that a process 
closely analogous to that which formed the older gneissic series was in operation, and 
gave rise to these banded mineral masses in the midst of rifted and broken strata of the 
older rocks after these had assumed their present attitude. The lithological resemblances 
between the older and the younger deposits are not less remarkable than their differences, 
and suflice to show the great similarity between the conditions which produced the vein- 
stones and their enclosing rocks. The latter, however, appear, in the present state of our 
knowledge, to have been deposited not only ona vaster scale but apparently in a hori- 
zontal or nearly horizontal attitude. 
§ 60. What are regarded as examples of calcareous deposits of the two ages were 
described by the writer, in 1878, as occurring at Port Henry, on Lake Champlain, in the 
State of New York. Near the town isa quarry whence limestone has been got for the 
blast-furnaces of the locality. “Here elongated, irregular fragments of dark hornblendic 
gneiss, from two inches to a foot in thickness, were found completely enveloped in crys- 
talline carbonate of lime. In 1877, five such masses of gneiss were exposed in an area of 
a few square yards. One of these, a thin plate of the gneiss, having been broken in two, 
the enclosing calcareous matter had filled the little crevice, keeping the fragments very 
nearly in their place. The carbonate of lime, which is coarsely granular, and contains 
some graphite and pyrite, is banded with lighter and darker shades of color, and one of 
its layers was marked by the presence of crystals of green pyroxene and of brown sphene. 
The contact of this mass with the surrounding gneiss, which is near by, is concealed. No 
serpentine was found in this limestone, though it abounds in a limestone quarried in the 
vicinity. About half a mile to the north is still another quarry, opened in a great and 
unknown breadth of more finely granular and somewhat graphitic limestone, which 
near its border presents three beds of two or three feet each, interstratified with the 
enclosing gneiss.” Of this it was said that “it presents alternations of lighter feldspathic 
and darker hornblendic beds, with others highly quartzose, and includes layers of a sul- 
phurous magnetite, which are, however, insignificant when compared with the great 
deposit of this ore mined at Mount Moriah, in the vicinity.” 
§ 61. While the great breadth of limestone interstratified with the gneiss was 
regarded as belonging to the ancient series, it was said of the limestone of the first-des- 
cribed quarry, that it “seems clearly to be a brecciated calcareous vein enclosing frag- 
ments of the gneiss wall-rock.' Reference was then made to similar observations in this 
vicinity described by Prof. James Hall in 1876, who, from this breccia of gneiss-fragments 
in an exposure to crystalline limestone, rightly inferred the posterior deposition of the 
latter, and was led to conjecture that it might belong to a newer geological series. The 
only evidence of this, however, was the enclosed fragments of the gneiss, which, in similar 
cases, had led Emmons and Mather to infer the eruptive character of these same lime- 
stones, regarded by the writer as endogenous masses or vein-stones. The great thickness 
of the interstratified limestone-masses which form, according to Logan, integral parts of 
the vast Laurentian series, and their geographical extent, were described in detail in the 

* Azoic Rocks, etc., pp. 166-167; also the Geology of Port Henry, Canadian Naturalist, x, No. 7, 
Sec. IIT., 1886. 5. 
