Mesozoic and Ccenozoic Geology and Palceontology. 157 



of about fifty miles, and a mean breadth of fourteen miles. The super- 

 ficial stratum is an argillaceous and ferruginous sand, of a yellow or 

 reddish color, with an occasional pebble or small bowlder of sandstone, 

 or a white, silicious sand. Beneath this superficial layer, occasionally 

 argillaceous beds of clay are found, of a yellow, blue, green, red or 

 variegated color. In some places this clay is from twelve to fifteen 

 feet in thickness. Below this stratum there is usuall}' found a red 

 ferruginous layer, from an inch to a foot in thickness. Beneath this 

 layer there is a j^ellowish brown sand, frequently containing a large 

 proportion of clay, all of which is barren of shells. Below these su- 

 perficial layers occur the various shell beds of Miocene sand and clay, 

 from which these authors described Tumtella quadristriata, T. ter- 

 striata, Natica lyerspectiva. Flssurella GatilUformis^ Area ^jrotracia^ 

 Lucina speciosa,, and Venus cortinarin. They also described, from the 

 Eocene greensand, JSfucula Galtelliformis, now Nuculana cultelliformis, 

 ISr. parva, and Cytherea ovata, now Diane ovata. 



In 1838, Mr. Conrad* said that the most northern locality known to 

 be decidedly of Medial Tertiary age, is in Cumberland county, N. J., 

 from whence the deposits extend southward in a very connected series, 

 and are spread over a large portion of the Atlantic seaboard. The 

 eastern shore of Maryland is chiefly composed of this and the superior 

 formations, but the greensand occasionally appears. The Medial Ter- 

 tiary occupies all that portion of the western peninsula south of a line 

 running from Annapolis to Fort Washington, on the Potomac, and 

 nearly all that part of Virginia which lies east of a line running 

 through Fredericksburg, Richmond and Petersburg, to Halifax, in 

 North Carolina, in which State the formation expands to its greatest 

 breadth. The lowest stratum of the Medial Tertiary is cla}^ the upper 

 stratum sand; and the intermediate strata are composed of sand and 

 clay, either pure or intermixed. The general sui'face of the country is 

 level, and it was originally covered with a forest of pine trees. The 

 western limit is bounded by a narrow strip of the lower, or Eocene 

 Tertiary, which reposes upon Cretaceous strata. He described, from 

 the iSliocene., 3Iya producta. Pandora crassidens, Pholadomya abrupta, 

 Panopoia americana, Corhula elevafM, Venus tetrica, V. ducateli, now 

 3fercena7'ia ducateli, V. rileyi, Cytherea metastriata., Spho&rella sub- 

 vexa, Saxicava bilmeata, Ilactra incrassata, M. subcimeata, Cardium 

 acutilaqueatum, Lucinli crenulata, Venus latisulcata. now Euloxa 

 latisiilcata, Astarte arata^ A. cuneiformis, A. perplana^ A. coheni. 



Fossils, Tertiary Formations. 



