SECTIONAL TRANSACTIONS.— K. 385 



The deductions from the tree pollen work provide a time-scale which can 

 be applied to the individual peat deposits. The stratigraphy and distribu- 

 tion of the peat areas make possible a linkage with late glacial and post- 

 glacial physiographic conditions. The peats so far examined include hill- 

 top peats, woodland peats, pond peats, and shore-line peats. Our results 

 agree well both among themselves and with the results obtained in similar 

 work on the Continent. It is not proposed in this paper to discuss the 

 stratigraphical aspect of the work. 



Mr. N. WooDHEAD and Mr. L. M. Hodgson. — Pollen analysis of Snow - 

 donian peats. 



Detailed analyses of seventeen peats situated in the Nant Ffrancon valley 

 and its tributary corries have been made. The peats vary considerably in 

 depth and extent, but show a homogeneous texture with ' forest ' layers in 

 most of the upland areas. They show an abundance of tree pollen, and their 

 pollen diagrams agree in the main with those established for the Pennines. 

 The deepest peat in Cwm Idwal has Pinus and Betula dominant, in the lowest 

 layer so far investigated, with Alnus and Corylus in association. Alnus 

 ousted Pinus, but soon died out completely, giving place to a Piyius associa- 

 tion remarkable for its high frequency (71 per cent.). This maximum 

 occurred, according to Scandinavian authorities, in the late Boreal time, 

 the upper limit of which is marked by decreasing Pinus and increasing 

 Alnus. The latter reached a second maximum in the moist Atlantic period, 

 but Pinus seems to have lingered in Caernarvonshire long after it had died 

 out in the North of England. As on the Pennines, Betula supplanted Alnus 

 in the drier conditions of the sub-boreal period, but Alnus remained abundant 

 in the wetter parts of the valley. 



Corylus appears more or less uniformly at all layers in all the peats. 

 Quercus pollen is uncommon. In view of the present distribution of 

 Fraxinus in woods near the sea, it is interesting to note that its pollen has 

 been found only in the lower-lying peats near the coast. 



Historical records show that the Forest of Snowdon was laid waste in the 

 reign of Elizabeth, and the valley is now almost treeless. 



Afternoon. 

 Excursion to Askham Bog. 



Friday, September 2. 



Joint Discussion with Section D (Zoology) on Biological balance in fresh 

 water (Dr. W. H. Pearsall; Dr. W. Rushton and Mr. H. D. 

 Slack; Dr. R. W. Butcher; Mr. R. S. A. Beauchamp and Mr. P. 

 Ullyott; Dr. L. Lloyd; Prof. F. Balfour-Browne; Dr. G. S. 

 Carter; Mr. J. T. Saunders; Prof. H. S. Holden) :— 



Dr. W. H. Pearsall. — The water-algal balance. 



Dr.W. Rushton and Mr.H. D. Slack. — Observations on the relation- 

 ships between the flora and fauna in the tipper part of a chalk stream. 



The paper records the results of weekly and bi-weekly samplings from 

 selected stations in a four-mile stretch of the River Test (Hampshire) over 

 a period of eighteen months, with a view to gaining information which will 

 lead to an improvement of the fishing conditions. 



o 



