PHYSICAL AND FAUNAL EVOLUTION 



71 



tion here contains remnants of the Lorraine fauna with Byssomichia 

 radiata and other types. These beds are clearly the lower Juniata, 

 for the base of the series is seen in contact with the Bald Eagle con- 

 glomerate not far away. The maximum thickness of the Juniata in 

 central Pennsylvania is from 1,000 to 1,200 feet. On the Niagara, 

 the corresponding Queenston shale is 1,100 feet thick, and it thins 

 away almost wholly before reaching Michigan, where only a few 

 red beds mark the summit of the Ordovicic. 



The Juniata has all the characters of deposits in arid regions. 

 The total absence of fossils, except where, at the beginning, a lagoon 

 extended north into Pennsylvania, is a striking feature. That 

 fossils could be preserved in the formation is proved by the occurrence 



AppslacHlan Bejlon 



Interior Refflon 



Marine Series Continental Series 



Fig. 10. — Diagram showing relationships of marine and continental upper Ordo- 

 vicic and lower Siluric strata. The conglomerate beneath the Juniata is the Bald 

 Eagle, and beneath it is the Eden sandstone. 



of Lorraine species in the basal beds. Their absence from the others 

 must then be taken as indicating that none were inclosed in the 

 strata. This absence of fossils, together with the character of the 

 beds, their red color, frequent mudcracks, and numerous clay slugs 

 or "Thongallen" in the sands, and the aeolian cross-bedding, 

 all point to a continental origin, under conditions of semiaridity and 

 tropical climate. That the Juniata and Queenston beds are equiva- 

 lent, and were formed under the same physical conditions, cannot 

 be doubted. Their correspondence in thickness indicates an almost 

 complete equivalency. They may, however, have distinct sources, 

 one in the southeast and the other in the north. In western New 

 York the Queenston shales are succeeded by the true Medina sand- 

 stones and green shales, which are partly fossiliferous, carrying a true 



