678 THE JOURNAL OF GEOLOGY. 



Pennsylvania, northwestern West Virginia and eastern Ohio may 

 be regarded as one, their details being unimportant in so far as 

 the present study is concerned. 



The trend of the anticlinal and synclinal axes is not N. N. E. 

 and S. S. W. throughout, for one of the great curves of the 

 Appalachian system is within Pennsylvania ; the axis of the 

 First Bituminous basin, for example, follows an almost W. S. W. 

 direction until, in Clearfield county, midway in the state, its 

 course is changed to S. S. W.; any topographical map of 

 Pennsylvania illustrates the condition. 



Interesting variations in the rate of dip are shown along a 

 line drawn from Pittsburgh, Pa., southeastwardly across the coal 

 area to the Cumberland field in Maryland, the contrast between 

 the terminal conditions being very great. At Pittsburgh, the 

 rate seldom exceeds one degree ; in the Connellsville sub-basin it 

 varies from four or six degrees along the lower portion of the 

 trough to somewhat more than ten degrees on the side of 

 Chestnut Hill, the increase in rate thus far being quite regular. 

 No further increase is found in crossing the second and first 

 basins, the dip even on the easterly side of the Alleghanies 

 rarely exceeding twelve degrees. But the extent of disturbance 

 becomes markedly greater at once after the Anthracite Strip has 

 been reached, for there dips of 20, 40, 70 and 80 degrees are 

 seen. 



The conditions observed along this line are not representative 

 of those throughout the coal area, for in all the basins, even in 

 those of the Anthracite Strip, the degree of disturbance eventu- 

 ally becomes less along the trend northwardly. The existence 

 of the anthracite fields themselves is due to a remarkable 

 decrease in violence of the disturbance, a dying away northward 

 of anticlines, permitting formation of broad synclines, which in 

 their turn act as do the canoe synclines of the bituminous areas, 

 which, rising, send the lower formations into the air. South- 

 wardly, the condition is markedly different ; for though the 

 extent of disturbance, except in the Anthracite Strip, decreases 

 rapidly, the decrease is due to depression of anticlines and not, 



