€ = 
1883, ] 235 [Claypole. 
the thickness of which is only approximately given here, there yet remains 
an immense mass, the subdivision of which is more difficult, but would not 
perhaps be impossible if sufficient time were allowed. 
[Tam unable as yet to say if these Cardiola shales extend far north and 
south, no exposures having been yet found. But the places above men- 
tioned trace them through the middle of the county from south-west to 
north-east, a distance of seven or eight miles. Their farther extension is 
very little less than certain. 
APPENDIX. 
Since the above paper was read I have spent a few hours with Prof. Le 
Cj White, now engaged in the survey of Huntingdon county. With his 
assistance I found the bed here described and most of its fossils near 
Huntingdon. The thickness, though shortness of time prevented meas- 
urement, seems also very nearly the same, 
Note on the Genus Rensselacria in the Hamilton Group in Perry Co. By 
HH. W. Olaypote. 
(Read before the American Philosophical Society, September 21, 1883.) 
The Genus Rensselaeria, Hall, was established to receive certain Brach- 
iopods, some of which were new, and others of which had previously been 
Known under other names. They were distinguished by their general 
outward form and certain peculiarities of internal structure from other 
Brachiopods nearly allied to them. 
The Genus Rensselacria is limited in Eastern North America to the 
Lower Helderberg and Oriskany groups, four of its twelve species oceur- 
ring in the former and seven in the latter. One only, a small species, 2. 
Johanni, Wall, has been described from the Upper Helderberg of Water- 
loo, Iowa. Of this Prof, Hall speaks doubtfully, referring it to this 
Senus only on account, of its external characters. 
Prof, Hall informs me that he has since that time removed this species 
from the genus. It is, therefore, rather surprising to find well-marked 
Specimens of Rensselaeria high up in the Hamilton group of Middle Penn- 
Sylvania. Yet the sandstone, so conspicuous a feature of this group in 
Perry and adjoining counties, yields, near its middle, a bed which is in 
some places little more than a mass of shells of a form which can scarcely, 
ifat all, be distinguished from R. Marylandica of the Oriskany sandstone. 
Tn some places this shell is found almost alone, but in others it occurs 
mixed with Spirifera formosa, or a species so like it that I cannot distin- 
guish them. This Spirifera is the most abundant fossil in the Hamilton 
Sandstone of the county, occurring sometimes in myriads. 
