[ 239 ] 



1l3alf:^an^1f30ur at tbc flDicroecopc 



Mttb /IDr. XTutfen Mest, ff.%S., ff.lR^/llb.S,, etc. 



The notes selected for the present issue of our Journal were 

 written by Mrs. Tuffen West, but the drawings, we believe, are by 

 Mr. West. 



Flint— The formation of Flint is a most interesting question, 

 in considering which great care must be exercised not to confound 

 together two things essentially distinct, viz. — the deposition of sili- 

 ceous material, grain for grain, in the tissues of living organisms, 

 which is a chemico-vital process ; and the separation of similar 

 material from its solution by. dead or dying organic matter through 

 a purely chemical action. That the tissues of some plants have a 

 selective power cannot be doubted, and indeed it is a very won- 

 derful power when we come to consider it. By what power is it, 

 for instance — unless one impressed upon it ab initio — that the 

 Diatom separates silica, and incorporates it so largely with its 

 tissues, w^hilst the Desmid will have nothing to do with it ? There 

 is an old and favourite puzzle with young folks. It is a model 

 ship, fully rigged, or something of the kind, enclosed in a glass 

 bottle, through the neck of which it never coiild have got, by any 

 amount of ingenuity or squeezing. Of course, the bottle, whilst 

 in the soft state, was formed around it. Just so with the Forami- 

 nifera referred to by Mr. Nicholson, p. 240. They either were 

 attached to some gelatinous organism, which has perished, or 

 have become enveloped in it ; whilst this decomposed, by mutual 

 affinity silica united with it, and the result is a flint. In connec- 

 tion with the remarkable state of preservation in which we find 

 these delicate organisms may be mentioned some experiments by 

 H. J. Slack and W. Roberts on " Colloid silica," reported in the 

 Transactions of the Microscopical Society of London, July, 1868, 

 p. 105. They found what appeared to be fungi in some pure 

 aqueous solution of silica, on w4iich experiments on Dialysis were 

 being made. This set them thinking, and by enclosing mouldy 

 cheese and other similar organic substances in the solution of 

 silica, they succeeded in obtaining fungi artificially fossilised, some 

 of which bore a remarkable resemblance to Moss Agates. It is 

 curious to note that such deUcate structures as these fungoid and 

 beaded threads are not torn or materially compressed in the 

 process of solidification of the colloid silica. In Mr. Roberts' 

 specimens, in which the solidification took place very slowly, the 

 fungoid plants look in as natural a condition as when they were 

 floating freely in the limpid solution. The remarkable Foramini- 



