THE IRON CONCRETIONS OF THE REDBANK SANDS 



O. W. WILLCOX 



Fort Hancock, N. J. 



In the accompanying illustrations (Figs. 1-4), reproduced from 

 photographs, are shown forms of iron concretions which seem to 

 deserve notice alike for their peculiar structure, great length, uniform 

 orientation, and effect on local topography. 



These concretions are to be found in immense numbers in the 

 Redbank sands of Monmouth County, New Jersey, a formation which 

 is here a quite structureless bed of loose, rather fine quartzose sand 

 about 100 feet thick, generally red in color from the decomposition 

 of glauconite formerly disseminated through it. The concretions are 

 most numerous near the upper part of the formation, and occur as 

 isolated individuals imbedded in the sand, as well as more or less 

 densely packed in groups. 



The primary type of these concretions is a very long, more or less 

 regular, hollow cylinder, which is generally straight and of unvarying 

 diameter, but which sometimes tapers very gradually and may be of 

 indefinite length. Single tubes have been observed which were more 

 than 20 feet long, but it is impossible to remove unbroken such great 

 lengths from the sand in which they are imbedded, owing to the occur- 

 rence of transverse cracks which divide them into irregular segments. 

 Fig. I is from a photograph of such a segment; the diameter of the 

 tube is 1 ^ inches. The smallest tube yet observed had a diameter of 

 \ inch; the largest tube of circular cross-section so far seen had a 

 diameter of nearly i foot. The interior of the cylinder is generally 

 filled with sand differing in no respect from the sand without; the 

 wall of the cylinder is merely the ordinary material of the sand-bed, 

 cemented together by iron oxide. While the cross-section of the 

 cyhnder is often circular, more frequently it is quite irregular. Still 

 more frequently the concretion is not a closed tube at all, but a corru- 

 gated sheet. 



Besides simple tubes like that shown in Fig. i, there are the poly- 



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