138 



herst, was, as Prof. H. found tliem, compact atul perfectly homo- 

 geneous, and no nucleus was visible. The other, a very fine 

 example of these claystones, from an unknown locality, was a de- 

 pressed spheroid, almost a perfect circle in outline, presenting the 

 markings which gave it the appearance of having been turned in a 

 lathe, with an appendage on one side, apparently another spheroid 

 attached to the principal one. 



On cutting this open and polishing the cut surface, it displayed 

 a concentric structure with slight variations in color. There was 

 no lamination ; the whole mass being perfectly compact, and the 

 lines of colors not sharply defined, but fading almost impercepti- 

 bly one into the other ; but the contrast of colors was sufficient, 

 in a favorable light, to exhibit unmistakably the concentric ar- 

 rano-ement of the material and the origin of ihe lines on the 

 surface which give these concretions so much the appearance of 

 works of art. There is a minute nucleus less than -J^ of an inch 

 in diameter. The first concentric layer exhibits its arrangement 

 about the nucleus in the form of an ellipse, assuming the spheroi- 

 dal form at the outset ; the succeeding layers extend the long 

 diameter more than they do the short one ; then a layer extends 

 over the long diameter and one side only of the short ; on the 

 other side of the now lenticular body, the layer terminates before 

 reaching the centre, and its edge makes one of the lines, that so 

 much resemble the marks of the turner's tool. Other layers are 

 added to the long diameter, only increasing the compression of 

 the spheroid, their edges making each a line on both sides. The 

 lines of color in the appendage before referred to are concentric 

 with the centre of the concretion, showing that that was not 

 formed around an independent nucleus as might be supposed by 

 the external appearance. 



The minute size of the nucleus, and its position outside of the 

 centre, render it very difficult to be found without great care, 

 and very liable to be destroyed by cutting or breaking the stone. 

 No failure to find a nucleus is sufficient evidence that the concre- 

 tion was formed without it. 



Mr. Stodder also called attention to another form of 

 clay concretion or segregation, which he saw some years 

 since in Windsor, Ct. 



