The Inaugural Address. 



281 



by which the chalcedony has been deposited in one important illus- 

 tration. 



In the case of flints, however, we have not to deal with lamina- 

 tions like those of an agate, though the problem has many points of 

 analogy with that of the formation of agate. 



We have on the other hand a singularly homogenous material, 

 marked, it is true, with variegations of tint when we examine the 

 interior, but the forms and contour assumed by flints are sufficiently 

 often recognisable as those of organisms to prove that we have not 

 in dealing with them to do with a simply inorganic product formed 

 in the heart of an already solidified rock, but with an organism con- 

 verted into flint by a process that has caused silica, accompanied it 

 is true by more or less of impurities, to penetrate every pore and 

 portion of the organism, and to preserve it in the place where it 

 once lived, or at least where its dead form once lay. Its very colour 

 is, in part at least, due to organic matter retained in it. In the 

 agates we were dealing with an exfiltration from within outwards, 

 an outward directed dialysis of the more easily flowing material. 

 It is possible that in the case of flint we have, at least in the majority 

 of cases, a very slow process of infiltration, involving a gradual 

 penetration and retention in the canals and pores of the organism of 

 the colloid silica originally contained dissolved in small amount in 

 the water of the ocean, or as alkaline silicate, or even possibly in a 

 more complex condition as a double silicate. 



II. — But we are anticipating in these statements the verdict o£ 

 the biologist as to the nature of flint. Microscopic research has 

 shewn both chalk and the flint that traverses it to be composed 

 nearly entirely of protozoic organisms ; the chalk consisting in a 

 very large degree of an aggregate of the minute cellular (or for ami- 

 niferous) Rhizopod (or root-like footed) class of creatures. These 

 minute organisms secrete a shell covering of carbonate of lime, in 

 certain rarer cases of silica, and some again secrete no shell — the 

 calcareous Rhizopods then must have existed through long ages 

 in countless billions at the bottom of the chalk ocean, and built 

 up by their remains the vast deposits which now rise around us in 

 our downs as chalk. Flints, on the other hand, show in their form,, 



