GEOLOGICAL SOCIETY OF LONDON. 



those chains. The first or most north-western ridge, has not 

 been traced far into the north-eastern hmits of the coal-field ; 

 the second is known to extend 125 miles from the northern 

 boundary of the state to a considerable distance within the 

 coal area, where it flattens down ; the third and fourth have 

 been ascertained to range 160 and 200 miles respectively, 

 penetrating still further into the carboniferous regions, and 

 there disappearing. The fifth and sixth have been traced 

 250 miles each from the county of Susquehanna, quite through 

 the coal area to the confines of Virginia ; but the seventh has 

 been found to range only sixty miles within the district de- 

 scribed in the paper, or from the southern boundary of the 

 state to the Alleghany Mountains, one of the ridges of which 

 is conjectured, however, to be a continuation of it. In the 

 southern limits of Pennsylvania these ridges are said to pro- 

 duce anticlinal hills and synclinal valleys ; but at the northern 

 extremity anticlinal valleys and synclinal hills, instances of 

 each occurring in the intervening or midway districts. Where 

 the inclinal lines constitute hills, they always consist of the 

 hard quartzose conglomerate ; but where they occur in valleys 

 they are always connected with the soft members of the coal 

 measures, or the softer beds of the inferior red shales. 



Confining his observations to the anthracitic regions, east 

 of Susquehanna River, Mr. Logan next describes their geo- 

 logical and physical structures ; but it is impossible to render 

 this portion of the memoir intelligible without the assistance 

 of very detailed maps. We can merely state, that the dis- 

 trict is divided into three troughs — called the southern, 

 middle, and northern anthracitic coal regions —by ridges of 

 the hard conglomerate, and that numerous minor lines of 

 disturbance, parallel to each other and to the separating 

 ridges, traverse the troughs. In the southern region, the 

 minor anticlinal ridges, five in number, present a more abrupt 

 acclivity on the north than on the southern side; and this 



