324 The American Geologist. May, i897 
its middle shows that the mandible at rliat point is about 
seven-sixteentlis of an inch in thickness. 
Other important features will probably be revealed when 
later finds shall have shown us the complete mandible. Fol- 
lowing however the plan previously adopted of relying main- 
ly on this member for the distinction of the species no error 
can be made in the recognition of this as a new one which I 
have pleasure in naming after its discoverer. 
ON THE GENESIS OF CLAY STONES. 
By H. W. Nichols, Cliicago. 
The appearance and mode of occurrence of clay stones are 
too well known to geologists to require attention here. It is 
all but universally agreed that they are formed by the segre- 
gation through solution in and re-deposition from circulating 
ground waters of particles of calcium carbonate originally 
thinly disseminated throughout the clay matrix in which they 
occur. Tlie clay stones are simply portions of the clay firralj' 
cemented by crystals of the segregated calcium carbonate. 
Owing to the compact texture of the clay, the crystallizing 
forces are so hampered that large crystals (such as occur at 
Fontainbleu in porous sandstone) cannot form and the con- 
cretion shapes itself solely in accord with the amount of ma- 
terial brought to it from different directions. 
The clays in which these concretions occur are sedimentary 
deposits which have formed in quiet waters. While some of 
the contained lime may be, and frequently is, comminuted 
lime rock or vein calcite washed in with the clays, other parts 
are in the form of the small molluscan and ])rotozoon shells 
which often flourish under such conditions to such an extent 
as to change what would otherwise be a clay to a marl. Such 
life existed even in the icy waters in which the glacial clays 
of the Champlain epoch were deposited. 
The glacial clays, besides the powdered lime rock and cal- 
cite and the shells which have grown in the muddy waters of 
the growing clay deposit, may contain as well the crushed 
or powdered fragments of such land and water shells as the 
glacier met with. In addition the glacial clay may contain in 
the form of rock flour many lime-bearing minerals, the basic 
