348 MESOZOIC FLORAS OF UNITED STATES. 



The large, broken masses of silicified wood are, unquestionably, remains of 

 vasculares or dicotyledonous plants or trees, no member of which, we believe, has 

 yet been observed in our ancient coal vegetation. These resemble, somewhat, the 

 silicified wood of the Portland Oolite, and like them, exhibit no marks of perfora- 

 tion by the teredo. 



It must be observed that all the genera to which we assigned the fossil plants of 

 Fredericksburg occur in the Oolitic group of Europe. For tlris fact we have the testi- 

 mony of M. A. Brongniart, of Saussure, Pliillips, Murchison, De la Beche, and many 

 others. 



It is undoubtedly to what is now known as the Potomac formation, 

 but not wholly to the Older Potomac, that the following description of 

 Messrs. Meek and Haj^den, made on May 26, 1857, refers: 



There is at the base of the Cretaceous system, at distantly separated localities 

 in Nebraska, Kansas, Texas, New Mexico, Alabama, and New Jersey, if not, indeed, 

 everywhere in North America where that system is well developed (at any rate east 

 of the Rockj^ Mountains) a series of various colored clays and sandstones and beds 

 of sand often of great thickness in which organic remains, excepting leaves of appa- 

 rently dicotyledonous plants, fossil wood, and obscure casts of shells, are very rarely 

 found, but which everj^vhere preserves a uniformity of lithological and other charac- 

 ters, pointing immistakably to a similarity of physical conditions during their deposi- 

 tion, over immense areas. " ' 



Mr. Philip T. Tyson commenced his official operations as State 

 agricultural chemist of Maryland in May, 1858. He recognized the 

 necessity of a geological survey of the State and devoted two seasons 

 exclusively to field work. The map accompanying his first report '' 

 shows how far he was successful in working out the general geology of 

 Maryland. He enumerates twenty-four formations, of which the "Cre- 

 taceous group or chalk period" includes Nos. 21 and 22 in an ascending 

 scale, and thus describes them: 



1. A tliick group of sands and clays of various colors, but prmcipally white, red, 

 and bluish gray, with some thin beds of ferruginous sandstone resting immediately 

 upon No. 5. In some localities it abounds in lignite derived from coniferous plants. 

 The bluish-gray varieties derive their color from the carbonaceous remains of plants ; 

 but we have not yet met with fragments of sufficient size for determination. 



o Descriptions of new species and genera of fossils, collected by Dr. F. V. Hayden in Nebraska Territory, 

 under the direction of Lieut. G. K. Warren, U. S. topographical engineer; with some remarks on the Tertiary 

 and Cretaceous formations of the north-west, and the parallellism of the latter ivith those of otjier portions of 

 the United States and Territories, by F. B. Meek and F. V. Hayden: Proc. Acad. Nat. Sci. Philadelphia, 1857, 

 Vol. rX, 1858, pp. 117-148 (see p. 133). 



b First Report of Philip T. Tyson, State Agricultural Chemist , to the House of Delegates of Maryland, 

 January, 1860 



