Llyn Arenig Bach Deposit, d'c. By Ilenry Stolterfoth. 915 



The result arrived at from the examination of this list proves 

 that no species has existed in the lake which is not now a living 

 form in some place or other, while I was able to gather in a short 

 time more living species than are to be found in any part of the 

 deposit except the peat. The large forms of diatoms do not 

 appear to have sunk to the bottom, but are spread uniformly 

 throughout the deposit. 



One of the variations amongst the larger forms of diatoms is 

 marked by Surirella biseriata being abundant at the top and 

 middle of the deposit, while replaced at the bottom by Surirella 

 splendida, and as we go down, Melosira nivalis becomes more 

 abundant, also Gomplwnema acuminatum. 



It would be a great advantage if more was known of the 

 relative thickness of diatomaceous deposits, and the position of our 

 specimens in situ, for from this wo might learn something of the 

 way in which one species replaces another. 



Such an immense mass of minute forms as are collected at the 

 bottom of Llyn Arenig Bacb, point to the fact, that a long quiet 

 age has passed since the lake was formed. How long, as yet no 

 man can sjiy. 



This spring (1880) I liavc again visited tlio spot with <lie hope 

 of making a more careful examination ; but, alas ! I found the lake 

 again full, and all the wondrous deposit at least ten foct below the 

 surface ; and unless something goes wrong with the ]>ala water- 

 works, there is little chance that human eye will again rest on what 

 may bo termed one of the secrets of the deep. 



