316 Carhoniferous Formation of Pennsylvania — Wasmuth. 
less separated; and the geutly dipping flanks or flexures of the 
synclinals must be assigned to the areas, involved by a special 
synclinal or anticlinal of comparatively small depth. 
The anthracite measures of Pennsylvania are distorted 
enormously. (See maps of the second geological survey of 
Pennsylvania.) The greater portion of the anticlinals has been 
swept away by erosion, thus separating a number of synclinals. 
The synclinals mostly are long and narrow, the result of 
enormous lateral thrust; consequently the dip of the flexures of 
the coal beds is steep and at an average more than thirty 
degrees. Some flexures dip slightly near their outcrops with 
increasing dip towards the bottoms of the basins; others dip 
steeply on their outcrops and the incline decreases toward the 
depth. According to the present developments of the southern 
field, there seems to be little prospect of gently dipping bottoms 
in this coal field, but gently dipping flexures near the synclinal 
axis have been developed on the mammoth bed in the Shenan- 
doah district, etc. 
I must state here that only limited opportunities for the 
examination of the structural geology of the anthracite region 
have been offered to me because such investigations require time 
and money ; they were principally confined to the southern field 
and a few collieries in the middle fields, but they were sufiicient 
to enable me to outline a "sketch" of the structural and 
economical geology of the anthracite coal bfeds. 
The synclinal of the mammoth bed in Kohinoor colliery 
consists of a number of rolls dipping about 8 to 15 degrees. 
From the bottom of the shaft toward the face of a gangway, 
then being robbed, numerous fractures of the coal bed of 
varying course and dip are visible on the ribs of the gangway. 
The thickness of the mammoth bed in the place of robbing 
and its neighborhood is stated to be about 50 feet. The 
average thickness of the mammoth bed in the Shenandoah 
district is stated by the second geological survey of Pennsyl- 
vania to be about 24 feet, bat the same authority states also 
that the mammoth bed in many places is 60 feet thick. 
(Transactions of the American Institute of Mining E gineers). 
I maintain that a coal bed of an average thickness of about 
24 feet cannot increase naturally to a thickness of 50 and 60 
feet within such a comparatively small area as the Shenandoah 
