8 GIRTY 



# 



In Pennsylvania, between the Lower Carboniferous and the 

 Coal Measures, intervenes, as is well known, the Pottsville 

 series, a group especially noted for its sand and pebble beds, 

 but often containing as well a large quota of shales, fire clays, 

 and coals. The thickness attained by the Pottsville in the 

 Appalachian region is in some cases upwards of 6,000 feet. 

 The Pottsville series occupies a position in the section corre- 

 sponding to the " Millstone grit" of the Central States, and the 

 evidence of paleobotany, wherever obtained, shows that the 

 "Millstone grit " represents the Pottsville, sometimes one portion, 

 sometimes another, for the name has been applied not so much 

 to the same bed as to similar beds occupying the same position. 

 In the Appalachian region the Pottsville series is richly fossil- 

 iferous in the wa}'^ of fossil plants, but furnishes as a rule few 

 invertebrates. The invertebrate faunas are, except in a few 

 instances, peculiar and restricted, and clearly indicate unusual 

 environmental conditions. The most frequent fossil is Naiadites 

 elongatus Dawson, with which are associated bivalve crustaceans, 

 such as Estheria, Lcaia^ and Ostracods ; while more rarely 

 fragments of Prestwichia, or Limuloids, or fish scales and 

 plates are brought to view. An occasional Pectinoid, almost 

 always of the type of Aviculipecten whitci, together, not infre- 

 quentl}'', with Lingida and Orbiculoidca^ indicates that these 

 faunas cannot be considered as owing their peculiar facies to 

 strictly fresh- water conditions. Possibly the water was brackish, 

 or else the impurity produced by decaying vegetation and acid 

 products resulting therefrom exercised a prohibitive influence 

 upon oceanic life. In a few cases strictly marine faunas have 

 been found in the Appalachian Pottsville. 



In Arkansas Branner^ and the geologists associated with him 

 worked out the following section, which has been somewhat 

 modified by later investigations, both as to terminology and 

 arrangement. Nevertheless, the form in which Branner pre- 

 sented it is better known and will sufllce for the present discus- 

 sion. The Carboniferous portion of the section contains the 

 following formations, in ascending order : Boone chert and 



' Arkansas Geol. Suiv., Ann. Rcpt. for 18SS, vol. 4 (Wasliington County), 

 iSyi, p. 26. 



