DESCRIPTION OF SPECIES. PP. 117 



Not a single s%)ecies of the very abundant and varied mol- 

 luscan forms of the Coal Measures passes up into the Uj)- 

 per Barrens, and the only genus from the lower measures 

 that we have ever seen in the upper, is Solenomya^ which 

 is represented by a form quite close to S. permlensls . 



A suite of specimens, representing about all the animal 

 life that we find in the Upper Barrens, was submitted to 

 Prof. James Hall, the eminent paleontologist of Albany, 

 N. Y., and he gave it as his opinion that there was nothing 

 among them which might not be of Permian age. 



We may next inquire whether we have evidence of any 

 considerable change which would suffice to produce an im- 

 portant effect, and alter the conditions which prevailed in 

 the lower beds, which all recognize as of Carboniferous age. 

 For this purpose we must turn to the general geology of 

 the district. From this we find, after ascending above the 

 Pittsburg Coal, and its associated coals the Kedstone and 

 Sewickley, two horizons which give evidence of extensive 

 physical changes. 



The first of these horizons marks the general sub- 

 mergence which produced the important limestones and 

 calcareous shales which occupy much of the interval be- 

 tween the Sewickley and the Waynesburg. We find no 

 plants until we reach the roof shales of the last named coal. 

 These shales, as we see from our analysis of the table, 

 contain nearly all the characteristic Carboniferous plants 

 which pass into the Upper Barrens, mixed with a great 

 number of new forms. The physical change here was not 

 sufficient to entirely alter the flora. 



The second horizon of changing conditions, is found in. 

 and immediately above the Waynesburg Coal. In the 

 rapid fluctuations in thickness of the clay parting of this 

 coal we see the first indications of unquiet, and of the ap- 

 proach of that much greater disturbance which produced 

 the important Waynesburg Sandstone which in its extent 

 and character gives ample evidence of wide spread change. 



The Waynesburg Sandstone often rivals the great Con- 

 glomeratic Sandstone, which forms the base of the Product- 

 ive Coal Measures in the amount of pebbles which it con- 

 tains. It is often 75 feet thick, and in expanse is co-extensive 



