these groups are found to the east of us, but gradually 
thin out toward the westward, and have entirely disap- 
peared before reaching us, e. g., the Schoharie Grit, of 
the Corniferous Period. Again, although we have numer- 
ous exposures of the Niagara Period in our county, never- 
theless, not all the groups composing it are found here, 
e. g., the Medina Sandstone, although extensively found 
in Oswego County, just north of us, is nowhere found ex- 
posed in our county. 
Of the numerous groups into which these seven 
periods are divided, fourteen are found in Onondaga 
County. A complete description of each of these groups 
will be given later, when we speak more particularly con- 
cerning the various periods. 
The rocks found in our county belong almost entirely 
to the class known as stratified rocks. Shale, slate, sand- 
stone and limestone, with the various combinations of 
these, as shaly limestone, calciferous sandstone, etc., form 
the prevailing kinds of rock. In addition to these, how- 
ever, we find a vast quantity of drift scattered over the 
surface of the county, and mixed with its soil. This drift 
is composed of many large and medium sized bowlders, 
together with a great deal of fine sand and gravel. In 
composition it is extremely variable, some of the bowlders 
are quartzytes, others are schistose, others micas, etc., but 
the greater portion are so different from any of the rocks 
found in place in our county that they must have come 
from some other source. We also finda great deal of cal- 
careous tufa, or travertine. Not only is this peculiar rock 
found in many places upon the surface, but in the form of 
stalactites and stalagmites it also covers the ceilings and 
floors of those caves found in the county. Marl is another 
substance that is found to a considerable extent. Many 
of our lakes are continually depositing it. Serpentine also 
occurs, although very sparingly. We will speak more 
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