Jfesozoic and Ccenozoic Geology and PalcBontology. 2i>5 



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 usualh' found a red 

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

 layer there is a yellowish brown sand, frequentl}- 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 Turritella quadristriata, T. ter- 

 striata^ Natica perspectiva. Fissurella catilUformis. Area protracta^ 

 Lucina speciosa^ and Venus corfinaria. They also described, from the 

 Eocene greensaud, Mueula Galtelliformis, now Nitculana eiiltelllfovmis^ 

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



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

 be decidedly of Medial Tertiar}^ 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 Mar^dand 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 surface 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 .iipon Cretaceous strata. He described, from 

 the Miocene, ili"^r«^roc??6C^a, Pandora crassidens, Pholadomya abrupta, 

 Panopcea americana, Corbula elevata, Venus tetrica, V. ducateli^ now 

 Mercenaria ducatelU V, rileyi, Cytherea metastriata^ Splicer ella suh- 

 vexa^ Saxieava hilineata^ Maetra incrassata, M. siibcuneata, Cardium 

 acutilaqueatum, Lucina crenulata^ Venus latisulcata. now Euloxa 

 latisulcata, Astarte arata, A. cuneifo7'mis, A. perplana, A. coheni, 



Fossils, Tertiary Formations. 



