714 GEOLOGY OF OLD HAMPSHIRE COUNTY, MASS. 



form was sometimes assumed in spite of a marked want of homogenousness 

 in the stratum in which the growth took place. 



In "a great number of exactly similar concretions, however, from other 

 localities, one finds as a nucleus some portion of organic matter — a fish, 

 shell, or leaf — whose shape determines the form of the concretion, except 

 so far as the same may be influenced by the texture of the bed in which it 

 is formed. Here the organic matter inclosed in the bed of clay or fine 

 sand gradually surrounds itself with an atmosphere of the products of its 

 own decomposition, which slowly expands outwardly — in a massive bed 

 extending equally in all directions; in a laminated one, most widely in tlie 

 plane of lamination — and ;imong these products of decomposition are some 

 which readily precipitate the carbonates when by the ordinary capillary 

 circixlation the latter are brought within their range. Thus as the waters 

 move to and fro in the bed they come from every direction into the area 

 of precipitation, and a solid dependent for its shape upon the contour of 

 this area is formed around the organic nucleus, oftentimes hermetically 

 sealing it and arresting its further decomposition; while, on the other hand, 

 it can not be doubted that many times the organic matter which formed 

 the nucleus and determined the deposition was wholly dissipated into liquid 

 or gaseous compounds before the process was far advanced. 



Such a nucleus, now wholly vanished, may have determined the 

 beginning of the concretions we are discussing, and the fact that Presi- 

 dent Hitchcock found always a distinct residue of inflammable organic 

 matter in his analyses of claystones goes far to sliow that such was really 

 the case. 



We can see several sources from which organic material may have 

 been, and was, introduced into the clays during and after their formation. 

 The country was without doubt heavily wooded before the advent of the ice, 

 and all the growth and surface soil were ground uji together in the till from 

 which the clays are derived, and afterwards, while the latter were forming, 

 an arctic growth had again overspread the hills and worms burrowed in 

 the lake bottom, as I shall show further on (p. 718); and finally, rootlets 

 pierce even such unpromising beds as these to great depths — 25 and 30 feet 

 in the till of the Western States, for instance, and similar instances are 

 given below. I have found them several feet deep in the clays, with a 

 concretionary accumulation of ferric hydroxid already commenced around 



