62 



SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY, 1916. 



by tho containpfl pLuit fossils, as well as by 

 considerable coiiimimited lignite, tliat in places 

 forms layei-s 5 to 12 millimeters thick. The 

 Calvert contains marine invertt^brates in the 

 immediate vicinity of this outcrop, and asso- 

 ciateil with the plants are Nassa peraltoides 

 Martin and Disci niscd htguhtis (Conrad), the 

 latter a species whicli occurs in shallow water 

 free from sand. 



FAUNA OF THE CALVERT FORMATION. 



The fauna of the Calvert ft»rmation is exten- 

 sive, particularly in the marls that overlie the 

 diatomaceous beds. In addition to the re- 

 mains of marine vertebrates, which are in gen- 

 eral wide-ranging and of little significance in 

 ecology, there is a considerable molluscan 

 fauna. From the Calvert of Maryland 2.35 

 species of Mollusca have been described. About 

 100 species have been recorded from the Vir- 

 ffinia extension of these beds, but this mmiber 

 will be considerably increased when the studies 

 of Dr. J. A. Gardner are published. Twenty- 

 tliree of the Calvert species have been identified 

 in the Florida Miocene (Jacksonville and Choc- 

 tawhatchee formations), where 40 per cent of 

 the fauna is common to the Chesapeake group, 

 resembling more specificallj' the faunas of the 

 Miocene formations younger than the Calvert. 

 From an analyses of these Maryland faunas 

 Dall,' a few j-ears ago, concluded that they in- 

 dicated shallow marine waters and temperatures 

 somewhat warmer than those of the present time 

 in the latitude of Maryland. Of the species that 

 persist in the existing fauna, the bulk are found 

 south of Cape Hatteras. I see no reason for 

 doubting Ball's conclusions, which obviously 

 preclude the ' ' cold ' ' or even the ' ' cool tempei-- 

 ate" conditions that have commonly been 

 considered as characteristic of the Chesapeake 

 group. 



The United States hydrographic charts give 

 the mean temperatiu-e of the surface water of 

 the Atlantic in the latitude of Maryland from 

 December to May as 55°, and from June to No- 

 vember as 71.5°. The figures for Massachu- 

 setts Bay are 45° and 63.5°, respectively. The 



^ Dall, W. H., Maryland Geol. Survey, Miocene, pp. cxxix-clv, 1904. 



figiircs for the vicinity of Beaufort, X. C, which 

 is immediately south of Cape Hatteras and 

 which would appear to afford conditions cor- 

 responding to Dall's qualitative estimate, are 

 65+ ° for Decemlicr to May and 76° for June to 

 November. If Dall's estimate is reasonably 

 correct it would indicate that the mean annual 

 temperature of the water in which the Calvert 

 molluscan fauna lived was close to 70°. The 

 mean for the year at the siu'face off the Mary- 

 land coast is 63°, and at Beaufort it is 70°, and 

 although the liottom temperatures are slightly 

 l(^ss than the surface tcmpiTaturcs they are 

 more unifoi'm and for shallow seas like the Cal- 

 vert would not be appreciably lower. 



FLORA OF THE CALVERT FORMATION. 



COMPOSITION AND ENVIRONMENT. 



The most abundant plant remains in the Cal- 

 vert are the siliceous tests of diatoms. These 

 have been much studied by diatomists, who 

 have identified a very large number of species. 

 I am indebted to Dr. Albert Mann for the state- 

 ment that the Calvert diatom flora indicates 

 a comparatively shallow, strictly marine habi- 

 tat with relatively wann or subtropical tem- 

 perature. 



The remains of land plants preserved in the 

 strictly marine beds of the Calvert arc few both 

 in number of species and in number of individ- 

 uals. As a result of the present study I am 

 able to enumerate 26 species — 16 from Virginia 

 and 17 from the District of Columbia, with 7 

 forms common to the two areas. The flora in- 

 cludes 1 pteridophyte (Salvinia), 2 conifers 

 (Taxodium and Pinus), and 23 dicotyledons. 

 Leguminous forms and oaks predominate, al- 

 though the cypress (Taxodium) is by far the 

 most common form at Richmond, where cone 

 scales and seeds as well as an abundance of the 

 deciduous twigs are preserved. 



Although this flora is so small it fortunately 

 comprises forms whose characters indicate very 

 clearly the physical conditions along the shore 

 of the Calvert sea. The accompanying table 

 indicates the most similar fossil and existing 

 species : 



