418 A. W. GRABAU PALEOZOIC DELTA DEPOSITS OF NORTH AMERICA 



the Martinsburg series is sufficiently arenaceous to be classed as a sand- 

 stone, and is separately mapped as such in the Chambersburg quadrangle, 

 where its thickness is 600 feet. It is here exceptionally hard, coarse- 

 grained, thick-bedded, and easily recognized. "This rock where fresh is 

 a greenish gray arkose, composed of grains of sand and feldspar; the 

 latter has been decomposed to kaolin, giving the rock a speckled appear- 

 ance. Toward the base it is interbedded with shale -and merges into the 

 shale below." 2T a In coarse, brown sandstone near the top of the forma- 

 tion large Plectambonites, Rafinesquina squamula, and Zygospira mo~ 

 desta were obtained, and in massive mottled yellowish green sandstone 

 merging into the overlying Juniata formation poorly preserved Rafines- 

 quina alter nata were found." 2T These faunas are correlated by Ulrich 

 with the Eden of Cincinnati and the Lower Lorraine (Frankfort) of 

 New York. I desire to call attention to the fact that the upper beds are 

 arkoses, indicating semi-arid conditions under which the original rocks 

 from which the sands are derived were disintegrated,* and that this 

 series grades upward into the overlying Juniata red sandstones and 

 shales, the character of which further indicates relative aridity of climate. 

 Stose and Swartz cite Ulrich's opinion that the typical Juniata of Penn- 

 sylvania is younger than that of Maryland, Virginia, and Tennessee, 

 which latter he regards as of the age of the Oswego sandstone of New 

 York, while the Juniata of central Pennsylvania is of the age of the 

 Queenston shales (Pawpaw-Hancock Folio, page 4). In his correlation 

 table, Ulrich places the red sandstones of Maryland, Virginia, and Ten- 

 nessee (Bays sandstone of the latter) even lower, making them the 

 equivalent of the Pulaski shales, and actually placing the Bald Eagle 

 sandstone at a higher horizon. The validity of this assumption may now 

 be considered. 



The basal beds of the sandstone series in the Mercersburg area, where 

 its thickness is 1,200 feet, are a soft yellow sandstone exposed on the 

 Mercersburg pike, IV2 miles southeast of McConnellsburg, and here the 

 following fossils have been obtained by Stose : 



1. Segments of undetermined cystid columns 



2. Plectambonites sericeiis (thin small variety) 



3. Lephlocoleus jamesi 



4. Calymmene calliccplialus 



5. Dalmanella multisecta 



27 Stose : Mercersburg-Chambersbm\g quadrangle, p. 10. 



* Marine arkoses are today forming in the Gulf of California, where the local granitic 

 rocks disintegrate under the arid climatic conditions due to the interception of the 

 westerlies by the coast ranges. Decomposition is practically absent, and the disinte- 

 grated material is transported by the exceptional sheet floods which occur in this region. 

 (See W J McGee: The formation of arkose. Science, n. s., vol. 4, 1896, pp. 962-963.) 



