1880.] NATURAL SCIEXCES OF PHILADELPHIA. 289 



be older than the formation just described, and shown by its own 

 characters to bear no trace of glacial agencies, we may conjecture, 

 without au}^ reference to the phmts of the lignite, a middle or lower 

 Tertiary age. From the steep dip of the beds, — a fact difficult to ex- 

 plain ,— and from the great resemblance of the plastic clays to those in 

 New Jersey, on the Delaware, the writer at first supposed them to 

 be of Wealden age. Some facts in connection with a gravel found 

 in Virginia and other Southern States, which, in both appearance 

 and position is ver}' similar to the Bryn Mawr gravel, were at first 

 thought to indicate a Jurassic age. But after a comparison with 

 the other lignite localities, and especiall}^ with that at Brandon, 

 where the fossils were shown to be of Tertiary age, this view can 

 hardly be sustained. The absence of shells or marine plants indi- 

 cates a period of inland waters, and the plants at Brandon belong 

 to a tropical climate. 



It is now suggested that the period of the lignite mny corre- 

 spond most closely with that called b}' European geologists the 

 Oligocene. Since, in the present state of our knowledge, it is obvi- 

 ously' unsafe to make the age of these lignite deposits contempora- 

 neous with any exact geological epoch, and as there is a possibility 

 of their belonging to some period not recognized elsewhere, it will 

 probably be wiser for the present to group them together under 

 the name of The Brandon Period. As more facts develop and 

 wider comparisons can be made, more certain conclusions will be 

 possible ; aiid it must be understood that the theories here proposed 

 are brought forward onlj^ as those which now appear best to ex- 

 plain the facts observed. 



Postscript. — Since the presentation of the above paper, the writer 

 has been in correspondence with Prof. N. A. Bibikov, of Augusta, 

 Georgia, who has recently discovered lignite in that vicinity. The 

 locality, called "Read's Brown Coal Mine,'' is in Richmond County, 

 two and a-half miles from Berzelia, and sixteen miles from Au- 

 gusta. It is described as h'ing back of the outcrops of gneiss and 

 limestone, and is apparently in a very similar geological position 

 to the Pennsylvania locality. Iron ore, plastic clay, kaolin, and 

 decomposed sandstone occur with the lignite. As in Pennsylvania, 

 the lignite was found in a plastic clay beneath 25 feet of a decom- 

 posed sandstone. Pour strata of lignite, separated by layers of 

 shale and clay, were found at a depth of from 30 to 45 feet from 

 the surface. A series of coarse and fine sands and clays under- 

 laid these deposits and were penetrated to a depth of 95 feet. 



