PALJEONTOLOGICAL REPORT OF GEOLOGICAL SURVEY. 541 



9 are generally of a coarser texture than those of No. 11; under the 

 microscope they appear covered with small whitish spots, which are ei- 

 ther very small shells or crushed grains of sand. 



In regard to the distribution of the shells, it is necessary to recall 

 here what we have said on the distribution of the plants. In the 

 shales, of two beds formed near each other, all the species cannot be 

 different, therefore, the change in them ought to be examined with the 

 greatest care, before we decide that a palseontological distinction is 

 impossible, because some species of shells or remains of fishes are 

 identical in both beds. 



Though the fire-clay of the bottom cannot give precise indications, 

 we may mention that below coal No. 9 this clay is thick — from ten to 

 twenty feet and more, and insensibly passes into a hard rock, resem- 

 bling a variegated limestone. At Hartford it forms along the river 

 true perpendicular cliffs. This particular hardness, thickness, and 

 color of the fire-clay, attracted lately my attention to a bed of coal, 

 exposed in a cut of the Pennsylvania Railroad, about three miles east 

 of Greensburg. Supposing that it might perhaps indicate an identi- 

 cal horizontal level with our No. 9 coal, I had the black roof shales 

 opened, and by examination found them to contain the same remains 

 of fishes as those enumerated above. This bed of coal, only one foot 

 thick, is separated, by limestone, shales, and sandstone, from another 

 thick vein of coal, which is exposed still higher, and it is in the vicin- 

 ity of this last coal, and just at the eastern end of the tunnel, that I 

 collected, in great abundance, and in a perfect state of preservation, 

 many species of shells which, after examination, Mr. E. T. Cox pro- • 

 nounced to be all of the same species as those of our 11th coal. Thus 

 we have here the thick, hard, colored fire-clay, and the remains of fish- 

 es of coal No. 9, and with the coal above it the characteristic shells 

 of No. 11, to show evidently the concordance of the geological level 

 at both places, in the Pennsylvania and western Kentucky coal-fields. 

 The veins of coal mentioned above, and exposed in the great cut be- 

 fore the first tunnel east of Greensburg, have evidently their place in 

 the great limestone of the upper Coal Measures of Pennsylvania — the 

 lowest about one hundred feet above the Pittsburg coal, the other some- 

 what higher, between two beds of limestone, of which the inferior is , 

 more than twenty feet thick. This is a new and remarkable coinci- 



