Maryland Geological Survey 15? 



Per cent of 

 very fine sand 



Light 94.6 



Heavy 5.4 



Total 100.0 



DESCRIPTION OF PRODUCTS 



A. Under the Hand Lens 



/. Coarse Sand 



Grains of glassy quartz and some opaque, subrounded but showing a glossy, pitted 



surface as if solution had acted on them. The opaque grains, which are probably a 



saccharoidal quartz of quartzitic origin, are penetrated by an ocherous stain of which 



there are traces on some of the other grains. There are almost no grains that look as if 



they had been well rounded before solution acted on them. 



//. Medium Sand 

 Much like the coarse, but there seems to be a somewhat larger number of rounded 

 grains in it. 



III. Fine Sand 

 Like preceding. 



B. Under the Microscope 

 I. Very Fine 



(1) Light 

 Quartz : feldspar = 90 : 10. 



The feldspars are striking for the predominance of fresh grains (probably mostly 

 sanidine) among them. Feldspars showing the characteristic kaolonization along 

 cleavage cracks are very rare. Some were observed that had small bands of glauconite 

 arranged along cleavage cracks. 



(2) Heavy 



Among the heavy minerals glauconite generally in weathered, brown, opaque grains 

 is the most common. 



Common. — Magnetite unusually abundant ; garnet very common ; epidote. 



Rarer. — Tourmaline, chlorite, staurolite, rutile, zircon, enstatite, kyanite. Striking 

 in this rock are the varieties of zircon ; besides the usual colorless to pale hyacinth there 

 are grass-green and smoke-brown zircons. 



77 Silt 

 The silt in this case differs markedly from the very fine sand in that much of the 

 limonite present has gone into the silt, while the very fine sand is made up mostly of 

 fresh primary mineral grains. 



/// Clav 

 The product called clay is here, as in all samples in which much limonite has been 

 formed by weathering, a very impure product containing, in addition to true primary 

 matter, much of this secondary limonite. 



Summary and Conclusions. — The principal features of this sample are : 

 (1) The prominence of the coarser sizes of sand and the marked lack 

 of sorting. The diagram (I, p. 169) is distinctly of the lagoonal type (cf. 

 A, p. 169, and E, p. 170) and therefore requires no special comment. It 

 may well represent the basal deposit of a transgressing estuary of a large 

 bay like Chesapeake Bay, or of a lagoonal body of water. 

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