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Geographical distribution of the plants of the United States Coal measures.

§ 48. There is no special remark to make on this subject. A comparison of the species found at different localities whose horizon is recognized, the same shows their geographical distribution. The different localities of one and the same geological age are placed in the same column of the table of distribution. On the third column (the Sub-conglomerate), for example, one hundred and five species are indicated as contemporaneous or occurring in the coal fields at the same period of time. It indicates also that about one third of these species are found at far distant localities, as in Arkansas, West Virginia, Alabama, Illinois, Kentucky, &c., some at a single locality, others at two, others at three or four. Addition of species to the column by new discoveries will by and by complete and more distinctly interpret the characters of the flora of the Sub-conglomerate.

It is the same case with the different stations indicated by the columns of the table. Long and continued researches at distant localities whose horizon is ascertained, afford points of comparison for the representation of the geographical distribution.

On this subject we have, besides those marked in the Sub-conglomerate, important points of observation for coal A.  In Illinois, at Mazon Creek, Morris, Murphysborough, Colchester, &c.; in Missouri, at Clinton; in Pennsylvania, at Cannelton and Pittston.  Of the plants of these localities, which I consider as representing a coeval flora, about three hundred and eighty species have been already obtained up to the present time. These materials afford ample means for comparison.

The station of Mazon Creek, that of Cannelton, and the Campbell's ledge of Pittston, are for the geographical distribution by far the more important; not merely for the abundance of the specimens obtained from each locality, but because they more fully represent than any other the characters of the vegetation of the time.

In all the other localities, the plants here described have been found in the top shale of the coal strata and, therefore, merely exhibit a diminutive part of the whole flora which may have contributed to the constituent of a coal bed, or the plants living during a fraction of the whole period of time necessary for that formation. But the nodules of Mazon Creek are derived from a stratum of soft clayey shale three to eight feet thick. The bed has been washed through centuries by the water of a creek. The heavy iron-stones in which the remains of plants are imbedded have been spread and heaped, mixed together upon a wide bottom; therefore, these nodules represent the vegetation of a whole or at least of a prolonged period. For this reason, as also for the more perfect preservation of soft fragments of plants, which are generally destroyed in the top shale of the coal beds, the flora of that locality is remarkably rich and important.

The plants at Cannelton are found in a lower bed of shale or shaley cannel coal, four feet thick, which is entirely taken out of the mines and carefully examined, in its whole thickness for the vegetable remains which it abundantly contains, and which, as at Mazon Creek, represent plants composing the flora of the coal during a prolonged period.

It is the same with those found in the shale of the Campbell's ledge near Pittston. This bed, four feet thick, is also entirely quarried out and searched in its whole thickness for the collection and examination of its vegetable remains.