ON CAVES. 97 
But plants help one another. A forest creeps along the 
hillside and the vale, destroys the life that will not grow 
below it, but itself exhausts the soil, and in time perishes, 
having, however, renovated the soil for other plants which 
were kept out so long. In the four and six course farming 
man recognises this. Many diseases are but growths which 
creep across the world, feeding upon the constitutions that 
favour them, and then die out. Could we but destroy the 
seed that lingers somewhere to spread again over an earth 
peopled by new generations. 
Shall we say, then, this is the difference? The individual 
has a term of life measured by the vitality inherent in himself, 
which cannot be wholly renovated. 
The species has no limit to its life, save that imposed by its 
surroundings, which, however, it renders unsuitable by using 
up that on which its life depends. This, however, can be 
renewed. But will the same life be there to take advantage 
of the renovation? That is the question in each case. 
The dying-out and migration of species thus becomes only 
the outward growth of the fairy-ring. 
The incoming of new species only the appearance of the 
wingless, colourless grasshopper in the Mammoth Cave. 
The CHatrman (H. Cadman Jones, Esq.).—I presume I need hardly put 
it to the Meeting that we should return our thanks to Professor Hughes for 
his very interesting paper, which it has been a great pleasure to listen to. 
After some communications have been read, it will be open to those whose 
studies have lain especially in the direction of the subject taken up to 
commence the discussion. 
Captain Francis Perris, F.G.S. (the Honorary Secretary). Among the 
letters received from those unable to be present this evening are the follow- 
ing. The first and second are from the Duke of Argyll and Professor 
Hulke, F.R.S., mentioning that they have read Professor Hughes’s paper 
with much interest, and adding that they have no criticisms to pass 
upon it. The third is from Sir J. William Dawson, K.C.M.G., F.R.S. :— 
“ McGill College, Montreal, 
“ March 16, 1887. 
“T beg to thank you for your kind communication of an early copy of the 
interesting paper by my friend, Professor McKenny Hughes, on Caves. 
am glad that Professor McKenny Hughes is applying his well-kuown acute- 
ness and discrimination to those modern deposits which have given rise to so 
~ much somewhat crude discussion and speculation. His paper on the Drifts of 
the Vale of Clwyd * I regard as one of the most valuable we have recently 
* Quarterly Journal of the Geclogical Soctety, February, 1887. 
