Maryland Geological Survey 167 



that a swift stream could deposit in its delta a sediment with so much 

 coarse material, but the type of diagram is too far from that of a delta to 

 make such a belief tenable. 



Before attempting to adjust these facts some of the peculiarities 

 observed under the microscope should be considered. Foremost among 

 these are the grains of what are called secondary quartz. Humus waters 

 are known to have a strong solvent action on silicates and on silica. The 

 brown, humus coloring of some of the grains of secondary quartz and the 

 envelopes of the same color surrounding some of the marcasite spherules 

 suggest the presence of such matter; yet no carbonaceous matter was 

 found in the bed. Moreover, while decaying animal matter might have 

 precipitated the marcasite, the apparently disseminated occurrence of 

 these spherules and the fact that in the field they were not seen to be con- 

 centrated about the fossils seem to demand some other agent. The 

 assumption of alga? would meet these conditions and be in harmony with 

 the general stagnant-water character of the bed. If, however, the pre- 

 cipitation of iron disulphide is attributed to the animal matter the 

 secondary quartz might be accounted for by the former existence of a 

 swamp overlying these beds from which descending humus waters could 

 have produced the secondary quartz, but the knowledge of these processes 

 is still too imperfect to permit of a very trustworthy explanation. 



While the assumption of origin in place of the quartz grains described 

 seems to be demanded by their internal structure it should be noted that 

 this interpretation meets with a serious difficulty, that is, the outer 

 form of the grains. This form is that of the normal quartz grains in the 

 deposit, in part rather rounded, in part angular. If they formed in the 

 midst of the bed it does not seem as though they could have found the 

 space to grow freely; they should rather have involved adjacent grains, 

 and the ends of the other grains so involved should give the secondary 

 grain a rough agglomerated appearance. On the other hand, if they 

 formed in some organic mold there should be more regularity and uni- 

 formity to their shape. Field sections throw little light on the problems 

 as there are only a couple of feet exposed both vertically and laterally; 

 the only character noted is the presence of fine horizontal clay films on 



