1878.] 3d49 | Platt. 
100 Unknown in “Middleburg Village. (6.) 
2 | Black shale. (5.) 
21 (Black shale ? ) judging by the surface. (4.) 
2 | Black slate. (3.) 
15 Unknown. (2.) 
Helderburg Limestone. Half a mile below Middleburg, at grist 
mill. (Makes falls in the Schoharie.) (1.) 
Section of the Palezoie Rocks in Blair County, by Mr. Franklin Plati and 
Mr. R. H. Sanders, of the Second Geol. Surv. of Penna., in 1877. 
(Communicated to the American Philosophical Society, April 19, 1878.) 
The following section of the Palezoic rocks, exposed in Blair County, 
was made by compiling the sections taken from the following points: 
From the summit of the Allegheny Mountains at Bennington along the 
Pennsylvania Railroad to Altoona for XII, XI, X, [X, and VIII. At Franks- 
town for VII. At Hollidaysburg for VI. At McKee’s Gap for V. At Tyrone 
and Spruce Creek Gaps for IV, III. From Spruce Creek to Tyrone Forges 
for II. The measurements are based on the railroad lines and from the 
topographical survey of Blair County. 
From the Mahoning Sandstone to coal A is taken from report H H. 
XII to VIII was measured by plotting on the railroad map the various 
cuts and measuring the rocks in each cut, and then projecting them over 
onto a section line. The projection of the various cuts onto the section 
line was most likely accompanied by a few errors but they would not make 
any material difference in the thickness. 
The entire thickness of VIT could not be measured at Frankstown, where 
the best exposure could be seen. A good measurement of VI was obtained 
at the ‘‘Chimney Rocks”’ at Hollidaysburg. 
The measurement of V taken along the railroad cut at McKee’s Gap 
gives a good measurement except the lower part which is concealed, and 
which should have the horizon of the ‘‘ Frankstown”’ ore in it. 
Tbe Medina Sandstone shows best on the Pennsylvania Railroad, east of 
Spruce Beech Tunnel. The remainder of IV shows best in Tyrone Gap, 
but the rocks are crushed and the measurement is not reliable. 
III a complete section of these slates do not show anywhere in the county. 
II the thickness of these limestones and dolomites is taken from a care- 
fully measured section along the Little Juniata from Spruce Creek to 
Tyrone Forges. R. H. Sanders. 
345/ 4/’ XTIT Lower Productive Coal Measures. 
223/ 1’ XII Pottsville Conglomerate. 
283/ XI Mauch Chunk Red Shale. 
1,274’ 4/’ X Pocono Sandstone. 
2,560/ IX Catskill Sandstone and Shale. 
6,519’ 2// VIIT Chemung, Portage, Hamilton, Upper Helderburg 
50/ VII Oriskany Sandstone. 
900/ VI Lower Helderburg Limestones. 
1,328’ 3’ V_ Clinton Red Shale. 
2,565’ 10/7 IV Medina and Oneida Sandstone. 
960/ III Hudson-River and Utica Slates. 
6, 600/ Il and I (?) Trenton, Calciferous and perhaps Potitsdam 
23,348’ Palezoic rocks exposed in Blair County. 
