160 THE COASTAL PLAIN FORMATIONS OF CECIL COUNTY 



Matawan formation, and is overlain conformably by the Aquia. 

 It is developed in Cecil county in a continuous belt some six or seven 

 miles in width, extending from the vicinity of Chesapeake City to 

 the Sassafras river. Throughout most of this region the Monmouth 

 formation is largely covered up by sand and gravel of the Columbia 

 beds. 



The Xavesixk Marls. — The outcrops of the Xavesink marls are 

 restricted to a series of more or less detached exposures occurring 

 along the Sassafras river and Bohemia Creek. On the Sassafras 

 river these exposures extend from Grove Point to a little beyond Cas- 

 sidy Wharf. Along Bohemia Creek the outcrops- occur in the lower 

 valleys of the small tributaries, especially along Scotchman Creek 

 and the little stream just east of it. Other exposures of secondary 

 importance occur in Pierce and Pond creeks. Of the exposures in 

 the Sassafras basin, three are of particular interest. The first one 

 is found about one mile and a half up the river from Grove Point. 

 Here are exposed about 20 feet of fine, slightly micaceous sand, 

 intermixed with other sand stained brown by iron so as to give to 

 the whole a mottled appearance. Within the iron-stained parts are 

 small pockets of gray-green glauconitic sand. The whole is so imper- 

 fectly cemented together that it quickly weathers down to a loose 

 deposit. Under the microscope the grains of sand are rather angu- 

 lar. Those from the more ferruginous parts are completely coated 

 with iron, while those from the lighter colored pockets are entirely 

 free from it. Glauconite is found in these lighter patches, giving 

 them a greenish tint. The outcrop can be traced in the bank around 

 the swamps beyond Cassidy Wharf, with only now and then a 

 break where the Columbia gravels completely cover it. The best 

 exposures occur near Ordinary Point. The thickness of the IvTave- 

 sink here increases to a maximum of 45 feet, and then decreases 

 rapidly and disappears under the lower terrace which forms the 

 point. This section shows a little valley in the ^avesink, some 25 

 feet deep, that has been filled with Columbia gravel. 



On the east bank of the creek above Ordinary Point the Navesink 

 formation appears again and can be traced, although the exposures 



