716 GEOLOGY OF OLD HAMPSHIRE COUNTY, MASS. 



form, and to precipitate carbonate everywhere along its border, preventing 

 its penetration inward toward the center. The latter forms are not found 

 in this region, but occur in clays of the same age and origin at Rutland, 

 Vermont. 



The common pipestem concretions — small, hollow tubes made of clay 

 or fine sand cemented by limonite, about the size of a clay pipestem— which 

 stand verticle in the clay, are plainly due to the passage of water through 

 holes made by small rootlets, and the latter can at times be still found in the 

 holes. At the AVapping cutting (see p. 695) I was able to lift up and bring 

 away broad, frozen sheets of the fine loesslike sand, one-half inch thick, from 

 30 to 40 feet below the top of the cutting, which showed the early stages of 

 this growth very beautifully. The wind had delicately sculptured the siu-- 

 face and left the incipient concretions projecting above the surface, as a knot 

 projects above the surface of a worn board, but of regular shape, like very 

 large checker-men, each with a small, central root hole, and each about l.J 

 inches in diameter and concentrically fluted with beautiful regular grooves, 

 between which rise the deeper yellow ridges where the iron rust Avas con- 

 centrated. When thawed, the whole bed could be blown off the surface of 

 the board upon which it had been placed for preservation. 



These ferruginous forms have been produced by decomposing organic 

 matters at the surface, changing iron rust to ferrous carbonate, which has 

 been carried down the root holes and precipitated around them and then 

 slowly changed to limonite. 



The simplest and commonest form of the calcareous concretions is a 

 sphere, like that making the center of the largest specimen shown in the 

 figure, which expands regularly to form perfect disks. (See PI. XX.) 

 That the slow translation of the fluids in the clay has to do with the 

 growth is indicated by the common occurrence of spectacle-like forms, as 

 shown in the plate, where two neighboring disks, as they approximate 

 by growth, mutually shield each other and so become connected only by 

 a narrow isthmus. That a foreign body may cause the growth, perhaps 

 simply by halting the solutions, is shown by the fact that the limonite pipe- 

 stem concretions become the centers around which the regular discoid 

 calcareous concretions have groAvn. 



The folded concretion figured (PI. XX) is most interesting as showing 

 that the regular growth could take place in the contorted clays, and this 



