MARYLAND GEOLOGICAL SURVEY 161 



are poor, around the banks of the swamp to the next point where the 

 Columbia gravels again lap down to the water's edge. 



At Cassidy Wharf there is another good exposure of 20 feet, which 

 shows the same characteristics as the one last described. The most 

 easterly trace of the Eavesink formation on the Sassafras river is 

 along the bank of the little stream just above this wharf; beyond 

 this it disappears below the Red Bank sands. 



The exposures of the Bohemia Creek basin are as a whole very 

 much inferior to those of the Sassafras river basin. Along Scotch- 

 man Creek the Navesink formation appears in the bottom of the 

 valley. In the west bank the Columbia gravels rest directly on it, 

 while at the mill, three miles from the mouth of the creek, the Bed 

 Bank sand comes in above. Here in the road-cut are exposed 

 four feet of gray greenish to fine white micaceous Navesink sand, 

 overlain by 12 feet of case-hardened Red Bank sand. The Navesink 

 is composed mostly of quartz grains and mica flakes, with now and 

 then a little iron coating the particles. 



On the north side of Bohemia Creek there is a small poorly exposed 

 outcrop found in the first valley east of the bridge, and also another 

 on the stream to the west of it. In these two localities the formation 

 appears very similar to that last described. On Mr. Harriat's farm, 

 just east of the bridge, some fragments of fossils were found and a 

 few were well enough preserved for identification. In this neigh- 

 borhood there are a number of deserted marl pits which have not 

 been worked for a number of years. 



Two miles south of Pivot Bridge, on a branch of Back Creek, 

 there is a section 55 feet high, showing at its base 20 feet of brown- 

 ish-gray, micaceous sand bearing glauconite. This deposit is Nave- 

 sink and is overlain by coarse reddish-brown, slightly case-hardened 

 Red Bank sand. 



The Navesink marls of Cecil county have furnished very few 

 fossils. However, some have been found on the banks of the lower 

 Bohemia Creek, especially on Mr. Harriat's farm. Here were dis- 

 covered Exogyra costata, Say.; Gryphaea vesicularia, Lamarck; 



Idonearca vulgaris, Morton; and Cardium perelongatum, Whitney, 

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