2 STEVENSON— INTERRELATIONS OF FOSSIL FUELS. 



geology. They were described first by Webster, then by Buckland 

 and de la Beche and still later by Mantell.^ The chief " Dirt Bed " 

 with erect stumps was recognized by all as a black loam with re- 

 mains of tropical plants, which accumulated where they grew. This 

 soil, about one foot thick, contains slightly rounded fragments of 

 stone and, as Webster showed, is the original matrix of the silicified 

 stems J for, wherever exposed, it contains trunks of coniferous trees, 

 partly in the black earth and partly surrounded by the overlying 

 calcareo-silicious strata. The intervals are very nearly the same as 

 those seen in recent forests and the erect stumps or stools of the 

 large trees with attached roots are in their original soil. Associated 

 with the coniferous stems are others of cycad-like plants, also 

 silicified. The same condition was observed at another locality, 

 where the dip is 45 degrees and the stems are vertical to the plane of 

 bedding. 



Mantell states that the " Dirt Bed " has a considerable quantity 

 of lignite and of waterworn pebbles. While the prevailing trees are 

 conifers, there is abundance of plants allied to Zamia and Cycas. 

 Many of the trees are erect, as if petrified during growth. The 

 roots are in the black clay, and the stems reach into the overlying 

 calcareous rocks. Just prior to Mantell's visit, a large area of the 

 " Dirt Bed " has been exposed preparatory to removal that the under- 

 lying rock might be quarried. Some of the trunks were surrounded 

 by calcareous earth ; the upright stems were only a few feet apart 

 and usually were not more than 3 or 4 feet high ; without exception 

 they are splintered at the top as though they had been wrenched or 

 snapped ofif. All are without bark and have a weather-worn sur- 

 face, resembling that of posts set between tides. Two other dirt 

 beds were examined by Mantell, who obtained cycads from both : 

 the principal bed is so little consolidated that he was able to dig 

 out several cycads and to prove that they are actually in siiti. 



^ T. Webster, " Observations on the Purbeck and Portland Beds," Trans. 

 Geol. Soc, II., Vol. 2, 1829, pp. 41, 42; W. Buckland and H. T. de la Beche, 

 " On the Geology of the Neighborhood of Weymouth, etc.," the same, Vol. 

 4, 1836, pp. 13-15; G. A. Mantell, "Geological Excursions around the Isle of 

 Wight," 3d ed., 1854, pp. 286-290. 



