THE DEVONIAN SECTION NEAR ALTOONA, PA. 625 



serves to a remarkable degree the characteristics by which it is dis- 

 tinguished in western New York. As already stated in the description 

 of the Hamilton formation, the Genesee shale has been seen between 

 Bellwood and Altoona, at the intersection of Fourteenth Street and 

 Thirteenth Avenue in the latter place, on the New Portage Railroad 

 I mile northwest of Newry, on the road midway between Claysburg 

 and Queen, and near Queen. It crosses the Pennsylvania Railroad 

 in the concealed space between a point 2,375 feet west of the Logan 

 Hotel and Twenty-first Street. At the above mentioned street inter- 

 section in Altoona a thickness of 80 feet was measured, and, as the 

 base of the shale was apparently not exposed, its thickness may be 

 greater. The upper part of the formation is exposed in the bank of 

 Beaverdam Creek, \ mile southeast of Queen, and its full thickness 

 at this point is about 75 feet. 



Nunda formation. — This formation has been known in the pre- 

 vious reports on the geology of Pennsylvania as the Portage. Accord- 

 ing to the usage of the U. S. Geological Survey, however, the term 

 " Portage" should be restricted to the Portage sandstone of the Gene- 

 see River section in New York, and the term "Nunda, " which was 

 introduced in the early New York reports, applied to the rocks 

 generally designated the Portage group or beds. 



The basal 100 or 200 feet of the Nunda formation are composed 

 of soft pale brown clay shale, which weathers to a dove color and 

 has a very perfect cleavage, splitting easily into large, thin, smooth 

 plates. In this shale Paracadium doris and Pterochaenia jragilis are 

 relatively abundant and come in immediately above the Genesee 

 shale. In passing upward through the formation, the rocks grad- 

 ually change from the shale above described to a pale greenish-gray 

 sandy shale which makes up the greater part of the formation. This 

 shale generally cleaves easily into thin laminae, but there are beds 

 of coarser character and less perfect cleavage. Evenly bedded layers 

 of hard, bluish, fine-grained sandstone occur, and some thin irregular 

 layers. These layers are generally from i to 6 inches thick, and 

 rarely i foot. They are especially abundant through the 100 feet 

 of strata beginning about 350 feet above the base of the formaiion, 

 and are well exhibited on the Pennsylvania Railroad in the third 

 cut about I mile west of the station at Altoona. (Sec Figs. 6 and 7.) 



