1 
498 PROCEEDINGS OF MONTREAL MEETING. 
Plate 28 is a photograph of the rock cut on the Pittsburg, Fort Wayne and Chi- 
cago railroad, a half mile east of Rochester, Beaver county, of a bed of shale under- 
neath the Lower Kittanning coal-bed. This is a little fresher exposure than figures 
1 and 2, plate 27—that is, the cut was made deeper, and the concentric forms 
started presumably from a fresh plane surface when the railway was constructed. 
The small concretions are prominent, but the grosser ones less pronounced. 
Figure 1, plate 29, is a view of the bluff at the roadside on the east side of Block 
House run, at New Brighton, about 50 feet below the Lower Kittanning coal-bed, and 
near the same horizon as the stratum shown in plate 28. The concentric features are 
not quite so conspicuous as in the other views, yet plainly shown. There is lack of 
homogeneity in structure shown by the presence of the hard sandy layer, but it does 
not appear to have any direct relation to the concentric features. 
Figure 2, plate 29, is a view in the recently opened clay quarry of Reese, Hammond 
& Co. of Bolivar. The quarry is in Indiana county, on the hill on the north side of 
the Conemaugh river, and the material shown in the picture is flint fire-clay. Large 
concentric protuberances like voleanic bombs may be observed on the face of the 
quarry. In some places these concretions are very abundant, and vary in size from 
a few inches to two feet or more in diameter. In some instances the concretions 
are almost entirely clay-ironstone, sometimes, near the surface, iron oxide or limo- 
nite, and frequently a mixture of the clay and iron in varying proportions. In 
some cases they are apparently as rich in clay as the surrounding mass in which 
they occur, and those in the view contain so little iron that they are used for mak- 
ing firebrick, which burn to a light cream color. While the occurrence of the clay 
ironstone nodules is evidently due to the segregation of the iron, the explanation 
of the clay concretions is not so clear. : 
The phenomenon gives rise to this question: Is the occurrence of concentric 
nodules due to the segregation of foreign matter, or is the segregation of foreign 
matter due to concentric structure? Is the segregation of material due to previous 
concentric structure in the homogeneous material? May not the shale concretions 
in above localities be due to the absence of circulating foreign material to segre- 
gate? This is put inthe form of a question because the writer has not sufficient 
evidence to establish an affirmative answer, but sufficient to raise the question as a 
possible aid to co-workers. Should it be answered in the affirmative, there still re- 
mains the query, What causes concentric structure in a homogeneous sedimentary 
rock? Are the centers of the nodules points of first induration which spread out- 
ward in circles, or final points of induration in a hardening mass, or due to other 
causes subsequent to induration ? 
During the reading of the above paper Vice-President Hmerson yielded 
the chair to President Orton. 
In the absence of the author, the following paper was read by W. B. 
Scott: 
NEW GEOTHERMAL DATA FROM SOUTH DAKOTA 
BY N. H. DARTON 
The next paper, in the absence of the author, was read by J. J. 
Stevenson. 
