224 Geolozy of Harpeth Ridge, Tennessee. 
of the Harpeth, we examined a well exposed section of about 
one hundred feet. Init, and between the red encrinal limestone 
and the shale, occurs a formation of limestone, of a dark color, 
filled with masses of chert, and in appearance resembling the 
“ corniferous” of New York. Although we had but a short 
time to examine it, I doubt not it is the same. By a reference 
to the reports of Dr. Troost, geologist of Tennessee, it will be 
seen that the strata of this region often run out, and others occur 
within the space of a few miles. No traces of the last mention- 
ed rock were found at the former place of examination, yet the 
whole region is strown with fragments of chert, which have 
doubtless been furnished from it. 
Another evidence of the identity of the shales is a stratum of 
limestone found in them. At the mouth of Eighteen Mile 
Creek, on the south shore of Lake Erie, eighteen miles from 
Buffalo, a stratum of limestone, three or four feet in thickness, 
may be seen projecting from the shale near the top of the bank, 
and having fallen in numerous masses on the beach. 
It contains large irregular masses of iron pyrites. ‘The shale 
at Harpeth contains a similar stratum of less thickness, but re- 
sembling it in structure and external appearances, except being 
somewhat darker, and contains similar masses of sulphuret of 
iron. 'The shale also contains pyrites in minute particles, and a 
considerable quantity of bitumen—both characteristics of the 
arcellus shale, the latter circumstance having led to numerous 
excavations in them both, in search of fossil coal. 
But the character of the shale, as well as that of the rock con- 
taining the chert, is satisfactorily determined by the two which 
succeed it, and cap the hills in this vicinity. These are the Gar- 
deau or Lower Fucoidal, and the Portage or Upper Fucoidal 
groups of New York. Mr. Hall in his report for 1840 remarks, 
that no formations in the state are better characterized than 
these, and that almost the only fossils they contain, are the Fu- 
coides graphica in the former, and F. verticalis in the latter. In 
both of the strata next above the shale, these fossils were respec- 
tively found, and so nearly resembling those of the Gardeau and 
Portage groups in appearance and position, as not to be mistaken. 
In these were also found those nodular concretions often met with 
in the other. Besides the composition, the peculiar olive color 
and . the external characters of these rocks are easily recog- 
nized, 
