IRON CONCRETIONS OF REDBANK SANDS 



249 



concretions has shown relations for which the author confesses his 

 inabihty to offer explanations based on hypotheses involving fortuitous 

 mechanical circumstances, or possible modes of circulation of water 

 containing the iron in solution. There is among all the phenomena 

 associated with these concretions but one, in producing which 

 mechanical influences can be suspected of having played a tangible 

 part. This is the noteworthy parallelism of their longer axes with the 

 strike of the formation, which suggests that shore currents or waves, 

 acting parallel to or impinging upon the ancient Cretaceous shore, 

 may have sorted into some definite arrangement the material the 

 decomposition of which 

 was later to furnish the 

 cementing bond of the con- 

 cretions. But the influence 

 of waves or currents must 

 have stopped with the 

 action requisite to govern 

 the orientation of the con- 

 cretions, and could have 

 played no further part in 

 giving them their observed 

 characteristics. 



The author is therefore 

 inclined to the hypothesis 

 which regards these objects as forms proper to the cementing material, 

 which will, under proper circumstances, be assumed in obedience to 

 impulses residing in its molecules. There is evidence tending to show 

 that these concretions have a fairly definite morphology. In many 

 cases it is possible to show with great probability that the various tubes 

 of the polychambered individuals were not synchronous in their origin. 

 In Fig. 8 is given a generalized cross-section of a three-chambered 

 concretion. The relations shown are thoroughly typical. It will be 

 observed that only one — the largest — of the chambers, A, is really 

 cylindrical in cross- section; the next largest, B, has the outline of a 

 segment of a circle which is cut by the circle A; the smallest, C, has 

 the outline of a segment of a circle cut by both A and B. From these 

 relations, and from the relative thickness of the exterior walls and 



Fig. 6. — Sketch of the ends of a group of con- 

 cretions seen in a railroad cut. 



