Nov., 1917J 



Concretionary Forms 



11 



the result of carbonaceous material draining in and solidifying — 

 lined or filled with quartz crystals, through which sphalerite 

 may be disseminated — containing well formed crystals of 

 sphalerite — or filled with a brownish, carbonaceous clay. These 

 last two are very rare forms. These cavities are objectionable 

 in building stone. 



We now pass to the concretionary forms found in the upper 

 ledges of the Buff Stone. 



Concretionary "Masses'". — Usually these forms appear as a 

 distinct, continuous ledge five to thirty inches thick and two 

 to five in number. They rarely disturb adjacent layers, there- 

 fore "contorted ledges" is a term more suggestive of their 

 structure. 



Fig. 3. "Concretionary Pebbles." 

 Sketched from a piece 5 x 12 x 3 inches. 



Concretionary "Pebbles. " — Frequently within the "contorted 

 ledges" are found bunches or clusters resembling a conglomerate 

 of rather large pebbles. These pebbles are usually round, about 

 one inch in diameter and other sizes and shapes occur. When 

 broken for cross section, they reveal a ring around ring structure 

 somewhat similar to that of an onion. 



Concretionary "Whorls." — A rare form in the Rucker 

 Quarries, but frequently found in other exposures of the thin- 

 bedded upper Greenfield Limestone. They appear as fine lines 

 drawn around a center then joining into one another. May 

 prove to be a fossiliferous form. 



How could rock material aggregate into these various forms, 

 especially in strata so evenly bedded? How could this occur 

 while all forms and strata are of the same rock material? How 



