THE PHYSICAL CONDITIUXS INDICATED BY THE FLORA OF THE 



CALVERT FORMATION . 



By Edwaiu) Wh.heij ]5erey. 



INTRODUCTION. 



The object of till' present paper is to give a 

 suminarv of the sniull flora preserved in the 

 Miocene diatomaceoiis beds vi the Calvert for- 

 mation in the District of Columbia and Virginia, 

 and more especiidly to discuss its l)earing on the 

 physical conchtions of the Calvert epoch. Sub- 

 sequent to the middle Eocene the next abun- 

 dant marine fauna preserved along tlie midtUe 

 Atlantic coast is that of the Calvert formation 

 of the Chesapeake group. ^Vlthough Miocene 

 faunas so low in the stratigrapliic column are 

 known south of Virginia only in the vicinity of 

 Porters Landing, Savannah River, Ga., closely 

 related but younger Miocene faunas extend 

 southward at least as far as Florida, where the 

 containing formation rests unconformably on 

 bods in which occur the warmer-water faunas 

 of the Apalachicola group. 



The change from the Apalachicola faunas to 

 those of the Miocene constitutes one of the most 

 striking faunal changes of tlie later Tertiary- in 

 southeastern North America, and its emphasis 

 by Diill and others has led to what I believe to 

 be a misconception of the rctil climatic condi- 

 tions of Calvert time. Likewise from the fact 

 that the conspicuous deposits of diatomaceous 

 ooze in existing marine waters are in the polar 

 oceans it has been unscientifically assumed that 

 the diatomaceous beds so cliaracteristic of the 

 Calvert formation must have been formed by 

 species which had a more or less comparable 

 environment. 



CHARACTER AND EXTENT OF THE CALVERT 

 FORMATION. 



The Calvert foi-niation, named l)y Shattuck ' 

 in 1902 from the Cidvert Clill's, in Calvert 

 County, Md., consists of 200 to 400 feet of 



' Shattuck, G. B., The Miocene [onnation of Maryland: Science, npw 

 ser., vol. 13, p. 906, 1902. 



2.s924°— IG 



diatomaceoxis cartli, sandy clays, and marls. 

 It is tyj)ic:dly developed in Maryland, wli(>re the 

 basal member (Fairhaven) comprises about 65 

 feet of diatomaceous earth, locally argillaceous 

 and showing occasional infhixes of sands. The 

 Calvert has been recognized in southern New 

 Jersey and Delaware. It is also well repre- 

 sented in Virginia but disappeai-s in the south- 

 ern part of that State by tlie transgression of 

 the St. Marys formation, which complctel}- 

 buries it in Nortli Carolina, overlajjping on the 

 crystalline rocks of the Piedmont Plateau in 

 some areas. 



FossU land jdants have been found in the 

 Calvert at Richmond, Va., in the District of 

 Columbia along the Penning road near the 

 District line, and at Good Hope IIQl. The 

 formation crops out on the Good Hope road at 

 a point near the top of the hUl, where a few feet 

 of light-colored daj^ (Calvert) rests unconform- 

 ably on the fossdiferous beds of the Magothy 

 formation (Upper Cretaceous) . The Calvert is 

 overlain by gravels of late Tertiary or early 

 Pleistocene age. This locality is one of the 

 most northwesterly points at which the Calvert 

 can be recognized with certainty, and it must 

 also have been near the hxndward margin of the 

 Calvert sea. No invertebrates are associated 

 with the plants at tliis outci-op. 



At the Richmond locality the Calvert con- 

 sists of very clayej^ diatomaceous earth 40 to 50 

 feet in thickness, which rests unconformably 

 upon remnants of the Eo(u>ne or ujxm the 

 underlying Lower Cretaceous or crj-staDine 

 rocks and is overlain by Pleistocene deposits. 

 That this locality also was lu^ar the shore lino 

 of tlie Calvert sea, as it is near the landward 

 limit of the existing Calvert deposits, is in<li- 

 cated not only I>y the more claj-ey nature of the 

 materials compared with similar diatomaceous 

 deposits elsewhere in the ('alvei-t formation but 



