Geology and Natural History. 



iicsia, the remainder beiiio- carbonate of limi 

 of the Eozoon shell is given under IV, that 

 ■r V, aiid that of the magnesite which pcnetr; 



(phosph. traces) 1-260 



: ■'>/,' (I Mineral Silicate injecting Paleozoic GrinoJds ; l.y T. 



Xvw 15runsAvick, lately examined microscopically !>y Dr. 



I- remains, including fragments of trilobitcs, i^asii r<'iKi.!s, 

 '! 'iitipods, and joints of small encrinal stems and plates; ihe 

 wiioie cemented by calcareous spar in a manner similar to many 

 "ru'anic limestones. He observed, however, tiiat tlie poio ('I' 

 the crinoidal remains were injected by a peculiar mineral, readily 

 'li^-tinguishable in thin transparent sections, or on surfaces wliich 

 hail been exposed to the action pf an acid, which dissolves the 

 carbonate of lime and places in relief the injecting mineral. The 

 minute structure thus revealed is precisely similar to that of 

 recent crinoids studied by Carpenter, and will soon be described 

 and figured by Dawson. Decalcified specimens exhibit a congeries 

 of carved, branching and anastomosing cylindrical rods of the re- 

 placing mineral, sometimes forming a complex network, which, 

 under the microscope, resemble the coralloidal forms of aragonite 

 known as/os/em, and present a frosted crvstalline surface. The 

 ?ame mineral, as observed by Dr. Dawson, occasionally occupies 

 larger interstices among the fragments, and was evidently depos- 

 ited before the calcareous spar which cements the whole mass. 



When this limestone is dissolved in dilute hydrochloric acid, 

 the residue, washed bv decantation, equals from five to six per 

 oent of the weight of the mass, and is seen under a microscope to 

 <'onsi8t entirely of the casts composed of the mineral just noticed, 

 mixed with alwut one-fourth of coarse siliceous sand. This matter 

 IS pale gravish-green in color, but when calcined becomes of a 

 onght reddish-brown, without change of form. Heated in a dose 

 tnbe it gives ofi" water, and becomes much darker in color. It is 

 partially attacked bv strong hydrochloric acid, which takes up 

 jnuch protoxide of iron- but is readily and completely decomposed 

 ^y hot concentrated sulphuric acid, leaving a skeleton of silica 

 ^hich, by a dilute solution of soda, is readily separated from the 

 intermingled grains, more or less rounded, of colorless vitreous 

 quartz. The - - , . 



't in the way just'mentioned, yi( 



