154 THE ICE AGE IN NORTH AMERICA, 



in this lake was 280 feet at Allentown and its outlet at Topton 

 was 500 feet above tide. The shore lines can easily be traced 

 along the whole distance. The overflow into the Schuylkill 

 carried floating ice and glacial debris into that river so that 

 considerable deposits of glacial material were made in some 

 places, notably at Norristown only a short distance above 

 Philadelphia. Much of the gravel in West Philadelphia is be- 

 lieved by Professor Williams to have come down the Schuyl- 

 kill through this channel, and through the Little Schuylkill, as 

 all the coal region drained by the latter was covered by ice. 

 The efficiency and comparative recency of the glacial ac- 

 tion over this "Kansan" area in Pennsylvania is well shown 

 at Morea, a few miles north of Pottsville, and only one mile 

 north of the extreme limit of glaciation at this point. Here, 

 for commercial purposes, the "Mammoth bed" of anthracite 

 coal has been stripped of its covering of "Kansan till." The 

 coal vein here outcrops in nearly vertical planes favoring the 

 percolation of water and the disintegration of the surface. 

 Beginning at the top the covering consisted of from six to ten 

 feet of sandy till with occasional bowlders five feet in diameter; 

 below this were eighteen inches of crushed anthracite entirely 

 fit for the market ; then came three-fourths of an inch of rotten 

 coal mixed with angular specs of slate; then one inch of sandy 

 clay with rolled and angular quart zite and slate pebbles; 

 then one-half inch of fine bright crushed coal ; and below this 

 the glaciated surface, shown in the illustration, the upper 

 three-fourths of an inch of which was so soft and fully rotted 

 that it could be scratched with the finger nail. Below this 

 was an indefinite extent of solid bright marketable coal. The 

 recency of the glaciation appears in the fact that south of the 

 glacial border, only one mile away, the coal is so disintegrated 

 as to be worthless for many feet below the outcrop. At the 

 same time the covering in the glaciated area is so sandy and 

 porous as to be very little protection to the surface of the 

 coal. 



