382 W. A. TARR SYNGENETK' ORIGIN OF CONCRETIONS IN SHALE 



tion than in the shales. With small animals like crustaceans, scorpions, in- 

 sects of a fleshy and very delicate texture, the preservation of form is still 

 more remarkable. They are found entombed in the middle of nodules, just as 

 if they were in life, or as if tliey had been transformed into stone vv^hile still 

 living. The fruits or nutlets are not flattened." 



Eemarking furtlier in regard to their preservation, he makes this com- 

 ment : 



"Yet as the animals and plants of soft texture . . . have not yet been 

 found in the shale of our American Coal Measures, it is evident that these 

 remains have been generally destroyed by maceration, and only escaped total 

 destruction by their entombment in these nodules." 



Certainly in such instances as these there can be but little doubt that 

 the fossil form was so completely inclosed before burial that the presence 

 of the superincumbent beds did not crush in the slightest degree the 

 organic forms. The iron carbonate of which the concretions are largely 

 composed was evidently deposited around the organism before further 

 sedimentation occurred. 



No doubt instances of equally well preserved organic remains within 

 concretions have come to the notice of many paleontologists and geol- 

 ogists. 



PHYSICAL FACTORS 



Shales are recognized as impermeable rocks. They form the cap for 

 most oil and gas pools, as well as the overlying rock in water-bearing 

 sands. The movement of water through such rocks is at a minimum. 

 Movement does not take place even along bedding planes, and without 

 movement of water the material in the concretions could not be aggre- 

 gated. 



When the concretions are largely silica and clay and are covered with 

 numerous calcareous fossils which are splendidly preserved, the difficul- 

 ties of explaining the source of the materials or accounting for an ade- 

 quate transportation agent, and explaining why the calcareous fossils 

 should be aggregated at that particular point and not be replaced by the 

 incoming material, make an epigenetic origin appear impossible. The 

 fossils are embedded in the material of the concretions in the Pennsyl- 

 vanian of Missouri. They have every appearance of having fallen into a 

 soft, jelly-like material and having been there protected from further 

 alteration or deformation. If the silica in the concretions had been in a 

 colloidal state, as the writer has shown to be the case for the chert in the 

 Burlington limestone, the numerous fossils in association with the con- 

 cretions is more readily understood. 



