506 ARCHEOLOGICAL INVESTIGATIONS—II [ETH. ANN. 44 
stratified or massive, like the limestone with which it is connected, 
or it may be in nodules, concretions, flattened disks, or irregular thin 
masses which roughly correspond in their position and direction with 
the stone with which they are interstratified. The principal forms— 
disks, nodules, or concretions—frequently conform to the stratifica- 
tion of the stone containing them; that is, they are arranged in strata 
or planes which are practically on the same level or slope as the 
matrix. Often, however, they are distributed at random, as if they 
had grown promiscuously. The nodules or concretions may be sym- 
metrically spherical or ellipsoidal, but are usually more or less flat- 
tened, even to thin disks or sheets. The outer portion of both the 
massive flint and the nodules, to a varying depth, is usually grayish 
or yellowish in color and granular or chalky in appearance as a result 
of the disintegrating action of air and water which penetrate to 
them. This destructive influence is more pronounced by far upon 
the inclosing limestone than it is upon the chert; consequently the 
former is gradually dissolved and carried away by percolating water, 
while the chert remains in the clay which was diffused through the 
limestone; and this being less susceptible to corrosive influences, 
settles down as space is made for it and remains at the bottom when 
the stone is carried away. 
The coarse varieties of chert usually have a yellowish tinge, due 
perhaps to oxidation of the included iron. Those of finer grain, 
whether massive or nodular, are usually gray, ranging from almost 
white to almost black beneath the weathered exterior; while the very 
compact forms present a great diversity of coloring through every 
shade of black, brown, yellow, red, blue, and sometimes purple or 
green, from minute quantities of included iron, manganese, and other 
substances entangled in the mass while it was forming or diffused 
through it after it had hardened. These colors may have definite 
limitations, may shade into one another, or may mingle indiscrimi- 
nately, so there will often be several tints within a small space. 
Occasionally coloring matter is entirely absent, in which case the 
stone may be pure white if opaque, or clear like chalcedony if trans- 
lucent. In the last, included carbon or other dark substances may 
give it the appearance of moss agate. 
While silica is the most abundant mineral in the earth’s crust so 
far as this has been penetrated, very little flint or chert, compara- 
tively speaking, is found as a distinctive rock until the limestones 
of the Devonian era are reached. In these it appears in considerable 
amount as irregular flattened disks of various sizes, sometimes segre- 
gated, sometimes merging with others in layers measuring several 
feet across; but it never appears in a continuous stratum, and is never 
more than a few inches thick. It is generally coarse, much seamed 
