58 The American Geologist. January, isgs 
A third section measured by Mr. Gresley, three miles dis- 
tant from either of these dififers so Httle from them that it is 
useless to give it. 
How perfectly this great coal-bed preserves the Pitts- 
burg type of structure, is shown from the following sec- 
tion sent me by Mr. R. L. Somerville, superintendent 
of the Georges Creek Coal and Iron Company, Lonaconing, 
Maryland. The locality is east of the Allegheny mountains, 
and 150 miles from Pittsburg. It is as follows: 
Inches. 
"Roof" coal with slate parting below 20 
"Breast" coal 6" of bone on top gi 
"Slate" I 
"Bearing in" coal 4V2 
Slate o^ 
"Brick" coal 16 
Slate oYa 
"Bottom" coal 15 
Total thickness of bed 12', 4^" 
This type of structure is practically universal over all of 
the Pennsylvania, Maryland and eastern Ohio area of the 
bed. The different members vary considerably in thick- 
ness, as for instance the gradual increase of the "breast" 
coal from three feet at Pittsburg to six at Brownsville, 58 
miles up the Monongahela river, or to seven and even ten 
feet in the Georges creek and North Potomac regions of 
Maryland and West Virginia, or a decrease may take place 
in the same to thirty and sometimes to twenty inches, as 
in the Wheeling and Bellaire regions, but each of the main 
sub-divisions can be distinctly recognized, so that whether 
at Fairfax Knob, on the summit of the Allegheny mountains, 
3,200 feet above the sea, or deep down in the centre of the 
great Appalachian trough buried under 1,500 feet of sedi- 
ments, the explorer can readily identify this great coal-bed, 
not only from its associated rocks, but from its stratagraph- 
ical elements as well, and often from even the fracture of the 
coal. I once had a practical illustration of this latter pecu- 
liarity of the Pittsburg seam. About the year 1880 a coal 
bed was discovered near the summits of the hills, south from 
Himtington, West Virginia, and on one of my excursions to 
