78 University Geological Survey of Kansas. 
it was formed after ore formation began, or simultaneously 
with it. 
Primary Chert.— Primary chert is light in color and bears 
many evidences of having been produced simultaneously with 
limestone. Its abundance is very great, so great in fact that 
few, if any, geologists have comprehended how great itis. It 
is found in places interbedded with limestone as regularly as 
one rock is ever interbedded with another. Elsewhere it is 
found in large masses which seem to cut across the bedding 
planes and occupy a vertical position in many individual lime- 
stone horizons, extending downward even for hundreds of 
feet from the surface without any interruption. The largest 
beds of chert known anywhere in the southwest mining dis- 
trict are found at Galena, where a single chert body has a 
north and south trend from northern Empire to Shoal creek 
at the Standley diggings, a distance of fully four miles. The 
width is variable, but is at least three miles in the widest 
place. Its thickness is unknown, as no shaft has passed en- 
tirely through it, and the only well drilled in it, a water well 
at Empire City, was drilled without a sufficiently accurate 
log or record being kept to give us definite information. The 
drillers told the writer that they had practically nothing but 
chert and a little limestone the entire depth of the well, which 
is in round numbers 1000 feet deep. Shafts have been sunk 
over 150 feet in depth with the same general conditions at the 
bottom and top. Probably this is the largest individual chert 
mass in the world. 
Chert areas grade into limestone areas laterally in a variety 
of ways, the most common being a gradation by which each 
rock is divided up into layers that overlap each other, thus 
permitting the two masses to join a little like the several 
bones of the human skull are united, or like the fingers of 
the two hands may be passed by each other. In this way it 
is impossible to locate the exact line of demarkation between 
a flint or chert area and a limestone area. Frequently the 
tongues of flint assume concretionary or rounded masses pro- 
ducing odd-shaped bodies elliptical in general outline. Often 
concretions have a cavity along the axial or central line, as 
though the silica of the flint was segregated around some 
