190 PROF. W. C. WILLIAMSON ON M INKKALIZATION. 



materials was aided rather than impeded if the organic body- 

 exhibited signs of incipient decay. According to him, an 

 increased affinity between the original organism and the 

 mineral replacing it was produced by that approach to decom- 

 position — whether the pseudomorph was to become calcareous 

 or siliceous. This fact is especially obvious when Silicium is 

 the material substituted for the original organism. 



One of the most interesting of the specimens I have met with 

 in connection with this mineralization by lime shows another 

 feature that I have not alluded to, namely, that the matter 

 which has filled up the cavity has, in many cases, a selective 

 power of its own ; it will select some tissues to which it will 

 unite itself most intimately, and pass unaffected through 

 others. The case to which I refer was one to which my atten- 

 tion was first called by my very old friend Professor John 

 Phillips. He gave me some nuts from the bog of Warren Pool, 

 Ferrybridge. Now these were ordinary Hazel nuts, and on 

 examining them I found that the outer shell was in the 

 ordinary state of the shells of nuts that we so frequently dig 

 out of peat bogs ; but when I came to break this shell and 

 examine the kernel I found that the lime had passed both 

 through the shell and its lining membrane or endocarp without 

 affecting them, but the kernel was wholly replaced by carbonate 

 of lime ; not only so, but as Professor Phillips pointed out, 

 the lime must have been deposited gradually, because it 

 actually broke with something of the conchoidal fracture 

 which, as you all know, the kernel of a nut will exhibit when 

 you break it. This, I think, was about one of the very best 

 that I have seen, but numerous similar illustrations have been 

 met with showing the selective power that the lime has ; in 

 this particular instance it had an affinity for the kernel of 

 the nut, but none for the shell — it went to the heart of the 

 thing, the attractive element being probably the quasi-colloid 

 protoplasm. 



I must call your attention to another most interesting case 

 of the fossilization of plants. I have at home a collection of 

 about 3,000 microscopic sections of fossil plants from the coal 

 measures of Lancashire and Western Yorkshire, varying from 

 seven inches in diameter down to others of small size. The 

 history of these specimens is sufficiently clear. The districts 



