ON CAVES. 21 



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 CHAIRMAN (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 PETRIE, 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 Daw^on, K.C.M.G., F.K.S. : 



McGill College, Montreal, 



"March 16,1887. 



" I beg to thank jou for your kind communication of an early copy of the 

 interesting paper by my friend, Professor McKenny Hughes, on Caves. I 

 am glad that Professor McKenny Hughes is applying his well-known 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 



* Qvarhrly Journal of the Geological Society, February, 1887. 



