266 GENEKAL GEOLOGY. 



marked difference from the country of the Lower coal- 

 measure on the one hand, and what is seen in the region of 

 the Upper coal formation on the other. But the section 

 occupied by this formation certainly possesses its own topo- 

 graphical peculiarities, which, when once a certain degree of 

 familiarity with this as well as with the other two formations 

 of the coal-measures is gained, thereby rendering practicable 

 a comparative study of these features, afford as satisfactory 

 and reliable landmarks in detecting the presence and in 

 tracing the limits of this formation, as are found associated 

 with any similar set of strata. 



It is not unusual to find along the outcropping border of 

 the Upper coal-measures a belt of rolling land, which 

 gradually merges into the more gentle undulations charac- 

 teristic of the Lower coal-measure region, and strongly 

 contrasting with the plateau-like uplands common in the 

 country occupied by the Upper coal formation, wherever that 

 formation is not concealed beneath the excessive accumula- 

 tions of detrital material pertaining to the post-tertiary 

 period. This broken tract is especially noticeable in 

 localities where the water-courses traverse the formation at 

 right angles to the general trend of its borders. In the 

 immediate vicinity of the larger water-courses, the uplands 

 are intersected by short, deep ravines, and their valleys are 

 bounded by more or less steep, rounded acclivities one 

 hundred and two hundred feet in height. However, these 

 more strongly marked topographical features are subject to 

 various modifications, although always of a local character, 

 and therefore, limited in extent. 



It is well known that the coal-measure series of rocks in 

 the State are traversed by more or less regular undulations, 

 which were communicated to the middle formations equally 

 with the others. As often occurs, the slight depressions 

 between the low swells in the strata, are occupied by the 

 softer deposits of the formation, and wherever the streams 

 take their courses through these shallow synclinal troughs, 

 it is common to find them margined upon one or the other 



