348 MESOZOIC FLORAS OF UNrrFD STATES. 



Till' large, lnokcu masses of silieilied wood are. iiiuiiiotionahly, reinains of 

 vasciilares or dicotyledonous plants or trees, no nienil)er of w hieli, we helieve, has 

 vet heen observed in our ancient coal vegetation. These resemble, somewhat, the 

 silicified wood of the Portland Oolite, and like them, exhil)it no marks of ]ieri'ora- 

 tion l>y the tei'edo. 



It must l)e observed that all the genera to which we assigned the fossil plants of 

 P>cdericksburg occur in the Oolitic group of Europe. P'or this fact we have the testi- 

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

 others. 



It is tindoii!)tedly to what is now known as the Potomac fofination, 

 but not wholl>- to the Older Potomac, that the following description of 

 Messrs. Meek and Hayden, made on May 26, 1857, refers: 



There is at the ba.se of the Cretaceous system, at distantly separated localities 

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

 ever^'where in North America where that system is well developed (at any rate east 

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

 of sand often of great thickness in which organic remains, excepting leaves of ajji^a- 

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

 fotmd, but which everywhere preserves a uniformity of lithological and other charac- 

 ters, pointing unmistakably 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 thick group of sands and clays of various colors, but principally 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 bhiish-gray varieties derive then color from the carbonaceous remains of plants; 

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



« Descriptions of new species and genera of fos-sils, oollected by Dr. F. V. Hayden in Nebraska Territory, 

 under the direction of Lieut. G. K. Warren, U. S. topographical ciigin(<T; with some remarks on the Tertiary 

 and Cretaceou.s formation.s of the north-west, and the parallelhsin of the hitU'r witli tliose of otlier portions of 

 the United States and Territories, by F. B. Meek and F. V. Hayden: Proc. Acad. Nat. Sci. Philadelphia, 18.57, 

 Vol. IX, IS.T,S, pp. 117-148 (see p. 1.3.3). 



'' First Report of Philip T. Tyson, State Agricultural Chemist, to the House of Delegates of Maryland, 

 January, 1860 



