189 



Dr. C. T. Jackson observed, that one of the specimens exhib- 

 ited was especially interesting, as it exhibited the rain drop im- 

 pressions in the tracks of birds' feet. 



Dr. C. T. Jackson exhibited a specimen of Allanite, a 

 mineral discovered recently in a new locality at Manches- 

 ter, N. H., by Mr. William S. Wilder. It was one of the 

 largest crystals Dr. Jackson had seen. It contained the 

 oxides of cerium, didymium, and lanthanium. Dr. Jackson 

 has an analysis of the mineral in progress. 



Prof. W. B. Rogers exhibited to the Society, two speci- 

 mens of Lignite, which had been referred to at the pre- 

 ceding meeting ; the one from the Middle Secondary 

 Rocks of Lancaster County, Pennsylvania, where it had 

 been found by Prof. H. D. Rogers, and the other from the 

 Coal-bearing Rocks of eastern Virginia. 



These specimens are interesting, not only as examples of the 

 beautiful preservation of woody structure in Lignite, but as 

 affording additional evidence of the close relationship between 

 the groups of strata in which they are respectively found. 



Both specimens are jet black, and, when broken transversely 

 to the fibre of the wood, present the smooth, conchoidal fracture, 

 and the lustre of anthracite coal. The longitudinal surfaces ex- 

 hibit the structure of the woody stem as perfectly as the finer 

 varieties of silicified wood, and what is chiefly important, the 

 details of structure are the same in both specimens. The most 

 prominent characters under the microscope, are, — 



1. The mass consists of elongated cells, with areolar markings, 

 and includes few or no proper ducts. 



2. These cells are intersected by thin, medullary plates, com- 

 posed of short cells, with similar, but more scattered markings. 



3. The areolae of the elongated cells are arranged in a single, 

 very rarely a double row, on each of the two faces which are 

 parallel to the medullary plates, but are entirely absent from the 

 other faces of the cells. 



In all these particulars, as well as in the dimensions of the 



