96 REV. Tl. O. HALL, F.S.A., OX A PIECE OF TIMBER, ETC, 



same time it is very desirable not to be led away by unreliable 

 and unsatisfaetoiy data, or "very rude estimates," such as Mr. 

 "Wallace fitly terms his own extravagant assumptions. 



The true naturalist will without doubt always feel more deeply 

 interested in the structure and formation of the beautiful sparry 

 deposit, the calc-sinter itself, than in the relative and uncertain 

 measure of the rate of the deposition of the carbonate of lime, 

 from which it is so wonderfully formed, in cave, or rock-crevice, 

 or mine. He will remember, as it has been well said,* that 

 *' The circulation of carbonate of lime in nature presents us with 

 a never-ending cycle of change. It is conveyed into the sea to 

 be built up into the tissues of the animal and vegetable inhabi- 

 tants. It appears in the gorgeous corallines, nullipores, calcare- 

 ous sea-weeds, sea-shells, and in the armour of crustaceans. In 

 the tissues of the coral-zoophytes it assumes the form of stony 

 groves, of which each tree is a colony of animals, and in the 

 wave-def)-ing reef it reverts to its original state of limestone. 

 Or, again, it is seized upon by tiny masses of structureless pro- 

 toplasm, and fashioned into chambers of endless variety and of 

 infinite beauty, and accumulated at the bottom of the deeper 

 seas, forming a deposit analogous to our chalk. In the revolu- 

 tion of ages the bottom of the sea becomes dry land, the calcare- 

 ous dihria of animal and vegetable life is more or less compacted 

 together by pressure and by tlie infiltration of acid-laden rain- 

 water, -and appears as limestone of various hardness and consti- 

 tution. Then the destniction begins again, and caves, pot-holes, 

 and ra^'ines are carved out of the solid rock." 



• Cavc-IIunting, Clin|i II., p. 71. 



