The Original Chazy Rocks — Braineyd and Seely. 32B 
In the western middle coal field, about 50 per cent. o£ the 
shipments are mined from other coal beds of the series and the 
rest from the Mammoth bed; and since the exhaustion of the 
thinner coal beds will progress rapidly, if the natural growing 
demand of coal shall be accompanied by an increased output, 
the only alternative which remains is to work the series of 
the smaller beds in the southern field too. 
Economical geology is based partly on the structural geology 
of mineral deposits because every disturbance of the deposit 
influences, more or less, either the quality or quantity of the 
product, or the expense of mining. The numerous small 
disturbances of the Pittsburgh coal bed influence only the cost 
of mining in a very minor degree. The disturbances in the 
anthracite beds influence quantity and expense of mining, both 
disadvantages increasing considerably, especially by dislocations 
of great extent. 
As the outcrops of workable coal beds have been exhausted 
extensively toward the synclinal, mostly by slopes; as the 
numerous flexures of rolls and dislocated parts of the coal 
beds should be worked economically by shafts and crossings 
of the strata in different levels; as such plants are excep- 
tions in the southern field; as the expenses of mining in- 
crease downward in geometrical progression, in the face of 
an inexhaustible supply of cheap bituminous coal in western 
Pennsylvania, etc., rigid economy will be forced upon the 
operators in the southern field at no distant day, and the 
principal remedy, it seems to me, will be the study, now 
almost totally neglected, of the structural geology of the an- 
thracite measures of Pennsylvania. 
4128 Elm Avenue^ Philadelphia, Pa., March, 1888. 
THE ORIGINAL CHAZY ROCKS. 
By Pres. Ezra Brainerd and Prof. H. M. Seely. 
The extent and importance of the Chazy formation in 
eastern North America appears to have been under-rated. 
Prof. Dana, in his Manual of Geology (III ed. p. 184) states 
that "the thickness in some parts of New York is 100 to 150 
feet." But in Chazy village careful measurements show a 
thickness of over 700 feet. The several varieties of these 
