DESCltll'TlON or TIIK SPECIES. 191 



bliUicc may indicatL' tliat trunk No. 1 came from the same locality. It is 

 silicifiecl in the same way and has the same kinds of scars. The casts of 

 the petioles in this fragment are rather larger than those of trunk No. 1, 

 being 22™'" by 12""" in cross-section. This fragment is shaped like an 

 irregular disk or (pioit, having the dimensions 26™" by 19""". 



TUUNK Xo. 2. 

 Platos CLXXIX, CLXXX. 



This was probably obtained from near Beltsville, being picked up on 

 the surface of the ground on Mr. Emack's farm. It is exactly like the frag- 

 ment found at Spring Garden, Baltimore, being even silicified in the same 

 way. The silica, replacing the vegetable matter of this trunk, contains a 

 large amount of iron, so that in proportion to bulk it is much heavier than 

 trunk No. 1. Curiously enough, both this trunk and the ferruginous frag- 

 ment found at Spring Garden show a projecting seam of ferruginous silica. 

 This is shown on the narrower side of the trunk on PI. CLXXX, and 

 less distinctly on the front left-hand side, on PI. CLXXIX. This seam 

 appears to be due to a crack in the trunk, which was filled with infil- 

 trated silica in the form of a vein. This silica in the projecting plate or 

 vein seems to be in part at least due to a partial filling of the ci'ack by 

 sand, for grains of sand are mixed with the silica deposited from solution. 

 On one side of the trunk near the top and close to the projecting silicious 

 plate, soldered to it and the trunk, are a number of small jjebbles coated 

 with iron. The sand and pebbles indicate that the original place of the 

 trunk was in sandstone, not clay, and this would cause us to infer that the 

 trunk was silicified in the lower Potomac sand. It would then come into 

 the upper Potomac or clay member only after the destruction of the sand- 

 stone or sand originally holding it. Trunk No. 2 is ovate in shape, and 

 decidedly narrowed towards the top. It is not so much flattened as No. 

 1, as is indicated in the view of the narrow side given in PI. CLXXX. A 

 small piece is broken away from one side at the top, but still this trunk 

 is more complete than No. 1. On the broader side, PI. CLXXIX, the 

 maximum height is 41°™, the greatest dimensions at base 35""", the shorter 

 dimension there 31"'™. The dimensions at the top before the breaking oft' of 



