Maryland Geological Survey 165 



SAMPLE NO. 13 (FIG. M, p. 169) 

 Serial number : 1. 

 Field number : 1-9-14-1911. 

 Formation : Rancocas (?). 

 Locality : South of Middletown, Delaware. 



Appearance : Coarse loose sand in a weak black clay matrix ; weathering shows it to 

 be full of marcasite. 



Mechanical Analysis 



Sample 9.257 gm. 



Per cent of 

 sample 



Sands » 76.8 



Clay 22.0 



Total 98.8 



Per cent of 

 total sands 



Coarse sand 9.5 



Medium sand 60.3 



Fine sand 18.1 



Very fine sand 6.9 



Extra fine sand 5.2 



Total 100.0 



Per cent of 

 very fine sand 



Light 91.4 



Heavy 5.1 



Total 96.5 



DESCRIPTION OF PRODUCTS 



A. Under the Hand Lens 



/. Coarse Sand 

 Grayish-white. Almost all grains are colored by black clay occurring in the 

 irregularities of the surface. The solution effect on these grains is evidently so strong 

 that it almost obscures the original form, producing a glossy but very irregular, deeply- 

 pitted surface. Most of the grains are of clear quartz but a few are granular in appear- 

 ance and stained dark grayish-black. A very few show dirty greenish staining. In 

 spite of solution effects it is evident that the majority of the grains were originally 

 rounded though there are some that as clearly indicate an original angular form. 



II. Medium Sand 

 Much like the coarse sand but with fewer rounded grains, few of the dark-gray granular 

 grains and with some heavy minerals (garnet, rutile ?, a black, very glossy mineral not 

 magnetite), etc. A little marcasite in the cleavage of some grains but no marcasite 

 nodules were found. 



III. Fine Sand 

 . Like the medium sand but with more heavy minerals (rutile especially conspicuous) 

 and the grains still more generally angular. 



B. Under the Microscope 



I. Very Fine Sand 



(1) Light 



Quartz : feldspar = 95 : 5. 



Feldspar much decayed. Of special interest are the dark-gray grains of quartz, which 

 appear to he full of black flakes like the argillaceous matter which forms the matrix of 

 the bed ; these quartz grains polarize as units. When they are crushed the fragments 



1 By summation of parts. 



