258 RODDY— CONCRETIONS IN STREAMS. [May 7, 



places in the stream channel being of concretionary origin as shown 

 by their shape, laminated structure, and composition. 



The finding of the new locality is of great interest. It shows 

 that a careful, intelligent, and systematic search will reveal these 

 formations in many other regions of the world wherever the proper 

 conditions exist for calcareous and sihceous precipitation through 

 the life processes of plants. 



But the geological significance of the great meadow deposits 

 also needs emphasis. The large accumulation in the Donegal Town- 

 ship Meadow represents a comparatively long period and this indi- 

 cates a considerable antiquity of the plants which form the concre- 

 tions. Then too, such a bed of closely packed concretions is highly 

 suggestive of the manner in which some ancient rock beds orig- 

 inated. For were such accumulations of concretions as those in 

 the Donegal Meadows to be consoHdated by the action of infiltrat- 

 ing waters, pressure, heat and chemical change solid rock beds 

 would result nodular in appearance and concretionary in structure 

 hardly distinguishable from the Hoyt Potsdam beds of New York. 



Species of the following genera of the Cyanophyceae are found as- 

 sociated with the calcareous concretions occurring in Donegal Creek, 

 Lancaster County, Pa.. : Glceocapsa, Microcystis, Coelosphcerium, 

 Aphanocapsa, Oscillatoria, Rivularia, Nostoc, Chroococcus. There 

 are also species of Protococcus, many species of Diatoms, sevei-al 

 species of Desmids, various species of the Chlorophycese, severai 

 species of Phseophycese, and species of Rhodophycese. 



