140 PHYSIOGRAPHY AND GEOLOGY OF THE COASTAL PLAIN PROVINCE. 



On Poo Eun just east of ''The Crater", marl is said to have been dug 

 a great many years ago for fertilizing purposes. Fragments of shells can be 

 picked up in the fields but no exposures of marl can now be seen, although 

 a short distance northeast from "The Crater" nonfossiliferous Miocene buff 

 sand is exposed. 



Shell marl belonging to the Calvert formation is found and has been 

 dug at Tinsberry Creek just east of the railroad crossing. It is said to be 

 of a very fine quality for fertilizing purposes as the shells are greatly 

 decayed and disintegrate soon after it is spread on the surface. Thus it acts 

 very quickly. The practice is to use about 250 bushels to the acre if there 

 is considerable vegetation on the land. If not, less is used, otherwise the 

 land would be ruined. Shell marl has also been dug in numerous places on 

 Ashton Creek and its tributaries. 



Four miles southwest of Bermuda Hundred yellow ochre was formerly 

 dug. The material was derived from the upper strata of the Calvert for- 

 mation. The ochre bed is said to be about 7^/2 feet thick on an average. 

 Specimens of prepared ochre and ochre from a pile near the mouth of one 

 tunnel were seen but none of it can now be observed in place. It was 

 worked by tunnels driven into the hill to a distance of 30 to 35 feet from 

 the surface. Bed ochre was manufactured by burning the yellow raw 

 material. It is said to have been more profitable to burn the ochre than to 

 dispose of the natural yellow material. 



Shell marl is poorly exposed along Marl Branch three-quarters of a 

 mile southwest of Carson and has been dug for fertilizing purposes along 

 the base of the hill near the branch. The shells occur in a matrix of gray 

 calcareous sand. The following forms were recognized: Pecten, Venus, 

 Crepidula, Area, Cardita, Venericardia, Astarte (2 species), Glycymeris, 

 Turritella, Crassatellites, Balanus, worm tube, Dentalium, Corbula ( ?) 

 Bryozoa, etc., etc. 



The Choptank Formation. 



(not RECOGNIZED IN VIRGINIA.) 



The Calvert formation is succeeded in Maryland by deposits of sandy 

 clays, sand, and shell marl that are much more arenaceous than the Cal- 

 vert below or the St. Mary's above. The beds composing this formation 

 decline in thickness toward the Potomac Eiver and are not known with cer- 

 tainty to occur on the southern side of the valley in Virginia. The deposits 

 hitherto described as Choptank in the Nomini Bluffs are now known, from 

 a more exhaustive study of both the stratigraphy and paleontology, to belong 



