884 Opinions upon Clay Stones and Coneretions, [S 
concretions in sandstone, and one notable one where in 
lets included between the cracks of an argillaceous sar 
concretions have formed, bounded by the polygonal sides of the 
cell. Unfortunately there is no word said as to the nature of the 
concretion, whether entirely like the rest of the rock, nor whether 
the entire sandstone partakes of this nature. Hè also alludes © 
crystallized bunches of quartz and pyrite as instances of comet 
tionary action, remarking that “this tendency in nature too 
centric solidification is so strong that no foreign nucleus ® 
needed.” i 
In the Text Book for 1883 he says much the same thing ® 
abbreviated form, referring with more doubt to the concretions 
character of basaltic columns, but defining the process as “te 
_ result from a tendency in matter to concrete or solidify aros | 
centers.” j J 
Le Conte, in his Manual of Geology, devotes three pages ® 
concretions, explaining them as occurring “ whenever any so : 
stance is diffused in small quantities through a mass of entire 
different material. Thus if a stratum of sandstone or clay we 
small quantities of carbonate of lime or carbonate of iron w 
through it, the diffused particles of lime or iron will gar 
a process little understood, segregate themselves into — 
less spherical or nodular masses, in some cases almost aas 
generally inclosing a considerable quantity of the material of 
strata. In this manner lime balls and iron ore balls n 3 
. ; In like maso 
so common in sandstones and clays, are formed. ; 
the flint nodules of the chalk were formed by the segregates 
silica, originally diffused in small quantities through the are 
sediment. Very often some foreign substance forms the | 
about which the segregation commences.” a 
Dr. Dawson, in a note upon cone in cone structures '® 
, po “ “they are 
Acadian Geology, says of ordinary concretions, + toe difai 
general attributed to the mutual attraction of particles wih 
through masses of sediment and aggregating te and 007 
solid bodies as nuclei, or flowing into cavities of fossils 
places of least resistance.” wat 
wm 
tates: “ That nodules are being formed in the e va f 
rocks now in the course of deposition. It is usual oe 
