Maryland Geological Survey 159 



SAMPLE NO. 11 (FIG. K, p. 169) 

 Serial number : 18. 

 Field number : 5-10-28-1911. 

 Formation : Monmouth. 



Locality : Seat Pleasant, Prince George's County, east of D. C. Line. 

 Appearance : A fairly light gray-black, fine-grained, very micaceous, argillaceous sand, 

 with many shells and shell fragments. This is one of the good fossil localities of the 

 Matawan. 



Mechanical Analysis 

 Sample 7.185 gm. 



Treated with dilute hydrochloric acid. 



Per cent of 

 sample 



Lime-free residue 94.8 



Lime (by difference) 5.2 



Total 100.00 



Per cent of 

 lime-free residue 



Sands 80.7 



Clay 18.9 



Total 99.6 



Per cent of 

 total sands 



Coarse sand 0.3 



Medium sand 2.6 



Fine sand 5.1 



Very fine sand 60.9 



Extra fine sand 30.0 



Total 98.9 



Per cent of 

 very fine sand 



Light 93.3 



Heavy 6.9 



Total 100.2 



MAGNETIC SEPARATION 



Attracted at 3000 ohms (mainly glauconite) 4.3 ' 



Attracted at 1000 ohms (mainly glauconite) 36.9 » 



Attracted at full current 13.0 



Non-magnetic 28.7 2 



Magnetite 17.4 3 



Total 100.3 



DESCRIPTION OF PRODUCTS 



A. Under the Hand Lens 



/. Coarse Sand 



(a) Three grains subangular to very well rounded, frosted. 



(b) Four grains likewise rounded but glossy and slightly pitted as though corroded by 

 solution. 



(c) Four grains rough, pitted, angular, corroded, with much greenish-black clay in 

 the irregularities of the surfaces. This shows a transition from (b), suggesting that 

 most of the grains were originally rounded, (a), (b) and (c) are of glassy quartz. 



(d) Sugary quartz, rough, fissured, pitted and filled with green glauconitic and black 

 clay stain. Four grains. 



1 Glauconite (see microscopic study below) may be taken about 37.5% of heavy = 2.5% 

 of very fine. 



2 Mainly carbonaceous matter. 



3 Note the unusually high magnetite. 



