C. Lloyd Morgan — Geological Time. 203 



pore ; and as they are also porous, to not over tliree-eightlis of an 

 inch of solid limestone. But a coral plantation has large bare 

 patches without corals, and the coral sands are widely distributed by 

 currents, part of them to depths over one hundred feet, where there 

 are no living corals ; not more than one-sixth of the surface of a 

 reef region is, in fact, covered with growing species. This reduces 

 the three-eighths to one-sixteentJi. Shells and other organic relics 

 may contribute one-fourth as much as corals. At the outside the 

 average upward increase of the whole reef-ground per year would 

 not exceed one-eighth of an inch." 



IV. Professor Huxley, in his admirable lecture " On a Piece of 

 Chalk," describes a specimen of Micraster in the Museum of Prac- 

 tical Geology, which aids us in forming some idea of the " period 

 which must have elapsed between the death of the Sea-urchin, and 

 its burial by the Glohigerince. For the outward face of the valve 

 of a Crania, which is attached to a Sea-urchin, is itself overrun by 

 an incrusting Coralline, which spreads thence over more or less of 

 the surface of the Sea-urchin. It follows that, after the upper valve 

 of the Crania fell off, the surface of the attached valve must have 

 remained exposed long enough to allow of the growth of the whole 

 Coralline, since Corallines do not live embedded in mud." " If the 

 decay of the soft parts of the Sea-urchin ; the attachment, growth 

 to maturity, and subsequent decay of the Crania ; and the subse- 

 quent attachment and growth of the Coralline, took a year (which is 

 a low estimate enough), the accumulation of the inch of chalk must 

 have taken more than a year." Professor Huxley adds, " On any 

 probable estimate — the Chalk period must have had a much longer 

 duration than that roughly assigned to it," on the supposition that 

 an inch of that rock could be formed in a year. Perhaps we may 

 take it as probable that a period of twenty-jB.ve years would be 

 sufficient for the changes to which the Micraster specimen testifies. 

 If so, we have no evidence that chalk may not be accumulating at the 

 rate of -^ of an inch per annum. More than this, in the present 

 state of our knowledge, we cannot say. 



V. With regard to Coal, Principal Dawson says that " we may 

 safely assert that every foot of thickness of pure bituminous coal 

 implies the quiet growth and fall of at least fifty generations of 

 Sigillari(s," so that if we follow Professor Huxley in the moderate 

 supposition that " each generation of coal plants took ten years to 

 come to maturity — then, each foot thickness of coal represents five 

 hundred years," or the material accumulated at the rate of a little 

 more than -^o of an inch per annum. Principal Dawson's assertion, 

 however, has reference to American coal, which is formed of the 

 accumulated stems of trees, but " undoubtedly the force of these 

 reflections is not diminished when the bituminous coal, as in Britain, 

 consists of accumulated spores and spore cases, rather than of stems," 

 and therefore we may fairly consider that iV of an inch is a high 

 estimate of the rate of accumulation of coal, and that perhaps i^o 

 of an inch would approximate more closely to the truth. 



VI. I do not remember to have seen any definite calculations 



