The Original Chazij Rocks — Brainerd and Seely. 329 
and in contact with the oolitic beds above. It appears also at 
the base of the wooded ledge on section I. 
The oolitic beds (Group B. 2,) are twenty feet in thickness, 
and never contain Maclurea magna, so common in strata both 
below and above. The weathered surface is covered with 
minute grains, like the roe of fish. No organic structure has 
ever been made out; but the mechanical origin of such concre- 
tions remains unexplained. This rock is a quite pure limestone, 
firm and fine-grained, and is extensively quarried in Isle la 
Motte as a marble. Polished specimens are beautiful, showing 
the outlines of crinoidal fragments. It is known in trade as 
" French Grey." 
The upper Maclurea beds have a thickness of nearly 200 feet. 
They are best exposed at Chazy in the central area, though they 
crop out at various points in the western area, as indicated on 
the map. The strata just above the oolitic beds furnish an 
excellent black marble, though at Chazy they have been 
quarried only for building stone, where they are crossed by the 
Tracy brook. 
Farther south-east in the pasture of Mr. Fisk is a bold black 
ledge (Group B, 4) covered on its eastern slope with embedded 
fossils of great Maclureas; while just beneath is a stratum 
containing masses of Stromatocerium two or three feet in 
diameter. This is known by the quarrymen as " curls," and is 
considered a blemish in the stone when used as floor tiles; 
though the graceful coil of the Maclurea is tolerated, and is 
often seen under foot in the corridors of our public buildings. 
The upper beds of Group B contain more or less earthy matter, 
and the rock has a mottled appearance after a few years expo- 
sure; and in ledges that have been long exposed, it often 
disintegrates into nodules an inch or two in diameter. 
The Strata of Group C. 
The upper group is as remarkable for its great variety and 
sudden transitions as the middle group is for its uniformity. 
It was all classed by Emmons with the Birdseye formation, to 
which some of the lower strata bear a marked lithological 
resemblance, the lines of calcspar having been erroneously 
identified with the Phgtopsis tubulosum of the Mohawk valley. 
The first twenty-three feet consist of repeated alternations of 
tough siliceous dolomite, and brittle pure limestone. It is well 
