18 THE POTOMAC OR YOUNGER MESOZOIO FLORA. 



on the Telegraph road. It is one of the most favorable materials known 

 to me in the Potomac formation for the preservation of good fossils. 



It is of course composed of undisturbed matter, unlike that found on 

 the road. The impressions in it are numerous and well preserved, but 1 

 was disappointed to find that they all belonged to a few species only. The 

 plants are nearly all ferns and conifers. The ferns show close affinity to 

 the most abundant of tliose collected by Meek at Baltimore, thus confirming 

 the indications of the lithology. These plants illustrate the curious local- 

 ization so common in the Potomac plants. Hardly a single species found 

 here occurs in the spot on the Telegraph road, the nearest affinity being 

 with certain Baltimore ferns and Dutch Gajj co)iifers. This spot will bo 

 referred to as "Hill-side near Potomac Run." 



In the w^oods that contain the last-described locality an interesting 

 occurrence of lignite is met with. The lignite is situated on a small stream 

 about one-fourth of a mile to the southwest of the plant-locality on the 

 Telegraph road. The stream exposes in its channel the lignite logs em- 

 bedded in dark gray clay. Tliis clay is a local deposit in tlie usual Potomac 

 sand. The lignite clearly was caused by the prostration of a forest in the 

 place where the trees grew. The trees may be seen for more than one hun- 

 dred yards along the bed of the run, lying at different levels, and mostly 

 turned iu the same direction. The logs are much flattened, so that a cross- 

 section presents the form of a much elongated ellipse. Some of the trunks 

 appear to have been originally fully two feet in diameter. 



This lignite, like all that found in the lower Potomac, seems to have 

 originated from coniferous wood, and at this place one species of conifer 

 appears to have furnished most if not all of the material. If we may judge 

 from the macroscopic character of the lignite, this tree grew in forests over 

 all of the Potomac terrane; for most of the lignite throughout the Potomac 

 of Virginia and much of that found in Maryland came from the same species 

 of tree. It seems to have had a wood of uniform and compact grain, with 

 numerous thin, closelj^-placed rings of annual growth. 



This lignite shows peculiar features that are characteristic of nearly 

 all found in the Virginia Potomac. When dr}', if it be split longitudinally, 

 the structure of the wood is beautifully shown ; but if a cross-fracture be 



