368 L. Lesquereux on the Coal Formations of N. America. 
places, generally increasing westward. Its greatest thickness, 
in the sharp Mountain near Pottsville, Penn., is 1100 feet.* 
sing D. Rogers's final report of the State Geol. Survey of Pennsylvania, vol. i, 
p- 109. 
_t In those coal regions of the United States where coal is abundant, a bed of 
bituminous coal is not remunerative, when under a thickness of three and a 
feet. In the Anthracite basin, the working becomes unprofitable for a bed of less 
than two and a half feet. 
