1 56 SCIENCE PROGRESS 



free-swimming reproductive spores might be liberated, and the old sponges dying 

 might be covered up. In the spring the reproductive bodies might settle down 

 to produce a new crop. There is, at any rate, nothing impossible in such a 

 course of events. But if so, we get a rate of rock formation of 300 or 400 feet in 

 100 years instead of one foot. Prof. Sollas's modest 26,000,000 years for earth 

 history is reduced to 86,666 or 65,000. To most geologists, perhaps, this will 

 appear as great a reductio ad absurdum as the one indicated above. Yet it 

 seems, on the assumption of periodic growths, the only possible solution. And 

 after all, there is no certainty either in Prof. Sollas's 26,000,000, or in the 

 100,000,000 arrived at by other lines of investigation. These figures — and, 

 indeed, much larger — are required by evolutionists, but they have not been 

 proved by geology. 



And the case of the. chalk flints does not stand alone in suggesting a quicker 

 rate of rock formation than one foot in 100 years. Without here bringing forward 

 details, it may be stated that every rock specially studied by the writer from this 

 point of view seems to indicate a rate of formation much greater than one foot in 

 100 years. But the chief point it is wished to emphasise is, that every rock may 

 be made to tell us something— quite roughly, of course, in many cases— of the 

 time it took in the making, if carefully studied. And further, that in not a few 

 cases the actual thickness formed in a year is made clear in the structure of the 

 rock itself. 



A reconsideration of the one foot per century measure is required. 



Since writing the above my attention has been kindly called by Prof. Grenville 

 A. J. Cole to a suggestion of his own on the subject of the origin of flint. "The 

 rhythmic deposition of flint," he says, " may be due to some action in a limestone 

 mass in which the silica was at first uniformly diffused." 



Prof. Cole also refers to the work of Liesegang on Geological Diffusion, on 

 which his opinion was founded. And he further points out that Liesegang himself 

 suggested an application of his experimental results to the explanation of chalk 

 flints. " Liesegang," says Prof. Cole, "compares the layers of flint with the zones 

 of regular deposition that occur in cases of diffusion of one substance through 

 another, and suggests that the silica in the chalk was formerly diffused fairly 

 evenly, and that a progressive one-sided precipitation then took place." 



The suggestion is an interesting one, and has a very important bearing on the 

 question of the origin of chalk flints. I have not seen Liesegang's paper, nor do I 

 know the details of Prof. Cole's suggestion, and so am not aware whether they 

 consider this segregation of diffused silica to be sufficient in itself, without the 

 periodic growth of sponges, to account for the facts. This is the important point 

 as regards my original note. If it is put forward as the complete explanation of 

 the occurrence of the flints in more or less regular layers I am afraid I cannot 

 accept it. If it is to be considered as a supplemetitary agency I think it is 

 absolutely necessary. So far as my chemical and physical knowledge carries me, it 

 appears to me necessary to have some definite starting-points for the segregation 

 of the diffused silica. A growth of silicious sponges would supply this. The 

 silica of the sponge mass might start the process, and thus determine the "local 

 habitation " of the flints. But it would require a considerable amount of diffused 

 silica deposited on the sponges to produce a line of flints. Here, then, the 

 suggestion of Liesegang and Prof. Cole would play its part. 



And there appears to be evidence that animal matter may start the segregation. 

 For in the chalk there are frequently found the tests of sea-urchins and bivalve 

 shells converted into solid masses of flint. 



