.^28 E. O. ULRICH REVISION OF THE PALEOZOIC SYSTEMS 



Chambersburg limestone section near Saint Thomas, Pennsylvania. — 

 A full section of the Chambersburg limestone in the most easterly of the 

 Mercersbnrg belts was observed 2 miles south of Saint Thomas. Xext 

 above the Caryocystites bed comes first 18 feet of granocrystalline, in part 

 minutely conglomeratic, bluish gray limestone, from which no recogniz- 

 able fossils were procured. Then 1 foot of similar limestone full of a ne^'- 

 Leper ditia, and above this the Beatricea bed, 15 feet thick, minutely 

 granular in texture and containing clayey pebbles in the upper part. This 

 last is succeeded by 53 feet of rock like that at Dickeys referred to the 

 Nidulites bed. It is overlain by the usual bed of granular limestone, but 

 here the early Trenton Sinuites fauna of the latter is uncommonly well 

 preserved and prolific. The Sinuites bed is followed by 31 feet of nearly 

 unfossiliferous calcareous black shale and thin black limestone, terminat- 

 ing above with a thin zone often filled with Corynoides gracilis and other 

 graptolites. Beyond this the bed grades upward into the typical dark 

 shale of the Martinsburg. The sharpest lithologic break in the upper 

 part of this section, as also in the Fort Loudon and Dickeys sections, 

 occurs at the top of the Sinuites bed. Ample grounds, therefore, exist for 

 referring the argillaceous limestone above this bed to the Martinsburg. 

 Kespecting the Sinuites fauna, it should be said that it is locally present 

 in the Chambersburg-Greencastle band at the base of the shale and just 

 above the zone in which the Christiania fauna is best developed. In the 

 section at Chambersburg this is at least 250 feet above the top of the 

 Nidulites bed, while west of Marion the interval is 400 feet or more. Evi- 

 dently it succeeds an important interruption of deposition, and for this 

 reason it is referred to the Martinsburg rather than the Chambersburg. 



Resume of differences between the Chambershurg and Mercershurg 

 belts. — Briefly recapitulated, the differences between the Chambersburg 

 limestone sections in the eastern basin and those in the Mercershurg 

 trough are (1) the presence in the latter of 150 feet or more of graa- 

 ular limestone containing an upper Chazy fauna never seen in the 

 former, (2) whereas in the Massanutten basin Chambersburg limestone 

 deposition, beginning locally with as much as 200 feet of Lowville lime- 

 stone, seems to have progressed steadily to the close of the Nidulites zone, 

 in the Mercershurg basin, on the contrary, oscillation caused (a) inter- 

 ruption at the close of the upper Chazy portion, (&) varying delay in 

 Lowville submergence, and (c) local discontinuity prior to the Nidulites 

 invasion, (3) while over 200 feet of Nidulites limestone and from 40 to 

 300 feet of interbedded shale and limestone, with the typical Christiania 

 fauna, and 0-200 feet of massive limestone, with a modified Nidulites 

 and Christiania beds fauna, were being laid down in the Massanutten 



