620 CHARI.es butts 



and Second Avenue, Altoona, extends thence northwestward to the 

 Pennsylvania Railroad at a point 1,425 feet west of the Logan House 

 and then follows the track to Kittanning Point. (See Fig. 3,) At 

 the base of the section the Lcwistown limestone of the Second Geologi- 

 cal Survey of Pennsylvania' is exposed. 



Oriskany sandstone. — This is thick bedded, generally coarse- 

 grained, gray or buff siliceous rock. The thickness seen did not 

 exceed 20 feet, and apparently it is not over 50 feet thick anywhere 

 in the region. Bowlders of this sandstone lie along the Pennsylvania 

 Railroad track about i mile southwest of Bcllwood, having slid down 

 from the outcrop on the hillside above. From these bowlders the 

 fossils given in the first list on a succeeding page were collected. 



In Altoona an outcrop of Oriskany was observed in an alley just 

 east of Fourteenth Street and between Third and Fourth Avenues. 

 At this outcrop, which is shown on the profile section, the weathered 

 rock is buff, fine-grained, and apparently argillaceous. It contains 

 the fauna of the second list beyond. 



At Duncansville, southwest of Altoona, the Oriskany is exposed 

 in a railroad cut and is thick-bedded and siliceous. (See Fig. 4.) 



Marcellus shale. — The Marcellus shale follows the Oriskany sand- 

 stone directly in this section, the Onondaga limestone of the New 

 York sections being absent as in all of the Allegheny sections south 

 of New York. So far as it can be identified, it is a black, highly 

 fissile, clay shale. It is certainly known only in a railroad cut about 

 I mile southwest of Bellwood. At that point about 20 feet of the 

 formation are exposed. Here the Marcellus shale apparently under- 

 lies the Oriskany sandstones, since the rocks are overturned and dip 

 to the southeast. In Altoona, shale showing in a thin outcrop on 

 Seventeenth Street near Third Avenue, and dipping 55° to the south- 

 east may be Marcellus, but there is no positive evidence that it is. 



Hamilton formation. — The Hamilton formation is predominat- 

 ingly a very dark green clay shale, which weathers, to a dull brown 

 or blackish color, and breaks up in weathering or under the hammer 

 obliquely to the bedding planes into very irregularly shaped pieces. 

 In addition to such rock, there is more or less shale approaching 

 olive-green and gray tints, and also dark green sandy and slightly 



I Report T on Blair County, by Franklin Pratt. 



