104 



TRANSACTIONS OF THE 



[1890 



Potomac. 



Variegated, mixed or broken, partly san- 

 dy clays above. Drab or lead-colored 

 beneath, stratified to water level, and 

 holding lignite and leaves of various 

 plants and trees - 



28-30 feet. 



Section in the cliff near bridge below the town of Upper 

 Marlboro, Prince George's county, Md. 



Miocene.. 



Yellowish sandy clay, becoming mottled 

 and of a more lead or pinkish drab \ 

 color below 15-20 feet. 



Eocene. 



Argillaceous greenish marl, rich in coarse 

 glauconite grains, with a few drifts of 

 ferruginous rock fragments, and some 

 pockets of coarse loose marl-sand 



Siliceo-calcareous dense rock packed with 

 shells and their casts imbedded in pale 

 greensand 



Underlaid by loose greensand and shells 

 packed in confusion 



Coarse greensand marl to bottom of 

 stream 



40 feet. 



5-8 feet. 

 3-5 feet. 

 2 feet. 



Section on branch at inner end of Swan Creek, entering 

 from the southeast. 



Quaternary 



gravel 

 Miocene? 



"1 



Pale yellow sandy clay, with some quartz 

 gravel on surface 



6-15 feet. 



Eocene. 



Cretaceous. 



Blue-black marl, very compact in most 

 parts, indurated below. Closely packed 

 bed of Turritella mortoni near top. Fol- 

 lowed, lower down, by scattered speci- 

 mens of Ostraea compressirostra and 

 Dosiniopsis meekii. Still lower down, 

 Latiarca gigantea, and occasionally Gar- 

 dita planicosta. Basal 15-20 feet beds 

 of larger Ostraea compressirostra 



60 feet. 



Argillaceous greenish marl running down 

 to black marl of the lower marl bed 



40 feet. 



