16 The American Geologist. January, 1892 
Maryland line, the Cherry Ridge shales have almost disappeared 
and the total thickness of Catskill, including doubtless some of 
the Montrose shale, is but 1980 feet. No outcrop is seen in the 
adjoining county of Somerset until the western edge has been 
reached, where under the great anticlinal of Laurel hill, the 
Youghiogheny river has cut down to the Delaware flags. There 
the Montrose sandstone is present, but only a few feet thick; 
while at not more than three miles further west, on the other side 
of the anticlinal, the Catskill has disappeared and the Vespertine 
(Pocono) rests directly on the Montrose shale. ; 
The Chemung shows a similar decrease in the same direction; 
for on the railroad section in western Bedford, the whole interval 
of Chemung and Hamilton is represented by a concealed space* 
of 2,630 feet, giving to the Chemung a thickness of somewhat 
more than 1,800 feet. The exposures under Laurel hill in the 
Youghiogheny and Conemaugh gaps suggest a continuance of the 
decrease, certainly in the upper portion. The gaps through 
Chestnut ridge, ten miles west from Laurel, afford the last ex- 
posures, in this direction, of any part of the Devonian on the 
eastern side of the basin; the section in the Conemaugh gap, 
barely fifty miles in a direct line from Pittsburg,t is 
Pocono 443° 
Montrose red shales 125% 
Lackawaxen conglomerate 20° 
Shale and sandstone 120’ 
Concealed to river 150’ 
The Montrose shale is composed of duil, grayish-red shale and 
thin streaks of sandstone, carrying Chemung species up to with- 
in one foot of the Pocono. The Lackawaxen is characterized by 
flat-pebbles as it is also on the ‘‘National road” in Fayette county, 
where some of the larger pebbles are felsyte-porphyry.{ Exea- 
vations made since these measurements were obtained show that 
there is much dull red shale below the Lackawaxen, especially in 
the concealed portion. The interval from the top of the Pocono 
*Stevenson, Geology of Bedford and Fulton counties, p. 81. 
+Geology of Fayette and Westmoreland Counties. J. J. Stevenson, 
Harrisburg, 1877, p. 291. 
An annoying error occurs in my report on the Ligonier Valley 
(Harrisburg, 1878). Part of the notes referring to this rock were copied 
under the Pocono, and some of the Pocono transferred to this; so that 
this conglomerate is described as not containing flat pebbles. 
EE 
