204 On the Origin of the Flints of the Upper Chalk. 



turned up. But, on carefully considering tlie matter, it be- 

 comes obvious that the chances are a million to one, comparing 

 human with cosmical periods, against the ' Challenger^ dredge 

 coming across any portion of the ocean in which that special 

 stage in the flint-formation had been reached, when the con- 

 solidation of the pectous silica was just commencing, or just 

 being completed. In all such operations of nature, we are 

 too apt to forget that, whilst time and money are said to be 

 almost convertible terms in human affairs, both time and 

 money are unknown at the bottom of the sea, except when 

 man has been either foolish or unfortunate enough to leave 

 there all that remains to him of these good things. 



EXPLANATION OF PLATE XL 



Figures 1 to 4 are diagrammatic representations of nodular masses of 

 black flint from the Upper or White Chalk (as seen in section), and are 

 intended to illustrate the mode of formation of the flint, its outer in- 

 vesting layer of chert, and other points referred to below. 



Fig. 1 represents the section of a spherical nodule of solid black flint 

 enveloped in its white or gre}dsh-coloured outer layer of chert. 



Fig. 2 represents the section of a similar spherical nodule, in which the 

 central portion of a mass of calcareous and possibly some sili- 

 ceous debris had been surrounded by the colloidal mass of pro- 

 toplasm and silica, the contraction of which upon itself had 

 been so great as to compress into a closely compacted mass the 

 contained materials, these having been converted into chert by 

 the incomplete replacement of their carbonate of lime by silica. 



Fig. 3. A similar section to the last, in which, however, the included 

 material was insuflicient to occupy the whole cavity, the vacant 

 portions having in all probability been occupied originally by 

 water. 



Fig. 4. A similar section to no. 2, having in the middle of its central 

 cherty mass a drusy cavity lined with crystals of pure quartz. 



Fig. 5 is a facsimile of the flgure given by Sir Wyville Thomson (at 

 p. 412 of his ' Depths of the Sea ') of ^'■Batki/hius,' as taken from 

 Prof. Hfickel's original drawing of a specimen examined by 

 him under the microscope, in a supposed living condition. This 

 figure is introduced here, not because I have ever believed in 

 the existence of Bathyhiics as an independent structure, but 

 because I regard the substance to which that name was given 

 as simple sponge-protoplasm, in order to show that even in the 

 dead state of this substance it is capable of exhibiting amoebi- 

 foryn outlines when subjected to gentle pressure. 



\ i. 



