460 J. BARRELL ORIGIN OF THE MAUCH CHUNK SHALE 



Organic evidences of subaerial exposure. — These may be divided into 

 evidences furnished by the animal and vegetable kingdoms respectively. 

 Of the first class the most famous are the tracks left by Sauropus pri- 

 mcevus near Pottsville, mention of which enters into all text books, and 

 which, at the time of their discovery by Mr Lea, in 1849, were the oldest 

 known amphibian footprints. Eogers states that they were found about 

 700 feet below the top of the formation, and adds : 



"About 1,500 feet lower in the formation tlie Geological Survey brought to 

 light another species of footprints of much smaller dimensions ; and soon after- 

 ward two other varieties, at a spot not far south of the West Branch gap in 

 Sharp mountain. They are always at the incohering partings between easily 

 separating beds of sandstone; and the indented surface is glazed with a fine 

 slimy clay, such as retreating turbid water leaves behind it. The scaling off 

 of this coating of clay soon obliterates the smaller footprints."* 



The present writer found another imperfect impression in a mud- 

 cracked stratum not far from the horizon of Sauropus primcevus. 



Supplementing this direct evidence of the presence of terrestrial life 

 is the statement made by Eogers in 1858, and which still holds good, 

 that the only marine fossils found within the formation are comprised 

 within the thin wedge of the Greenbrier limestone, beginning at its edge 

 in Cambria county and passing thence southwardly through Somerset 

 county to Maryland, f Farther south, as well as in the Shenango shales 

 of northwestern Pennsylvania, marine fossils of Chester forms have been 

 found in strata which J. J. Stevenson regards as contemporaneous with 

 the Upper Mauch Chunk. J Beside the footprints, the only evidences of 

 animal life noted hj the writer were worm tubes in the shales, crooked 

 and rambling, filled with a soft and more lustrous material, distinguished 

 from plant stalk impressions by the lack of straightness, and from roots 

 by the lack of attached rootlets. In addition, there are occasionally 

 other markings whose origins have not been positively identified. Rogers 

 gives an example of one of these which he thinlvs may be the trail of a 

 mollusk.§ 



The vegetable kingdom also furnishes its share of evidence, probably 

 no less positive in its nature, if understood, but in regard to the proper 

 interpretation of which it is more difficult to be assured. On these 

 Rogers makes the following notes : 



"The only organic remains ever met with in the Umbral red shale of our 

 eastern coal fields are some rare impressions of a large plant-like foi-m, dis- 



• Geology of Pennsylvania, vol. li, part li, 1856, p. 831. 

 t Ibid., p. 832. 



X Notes upon the Mauch Chunk of Pennsylvania. American Geologist, vol. xxix, 1902, 

 p. 248. 



i Geology of Pennsylvania, vol. il, part 11, p. 832. 



