Manchester Memoirs, Vol. Ivi. (19 1 2), No. Itt- 5 



Naviaila [viridis}']) were recognised ; also straight sponge 

 spicules. In the purer overlying clay the same two 

 diatoms, also a third {Navicula \elliptica\}) were found, as 

 well as sponge spicules. 



The relation of the layers of peat and upper clays is 

 well seen in a section at the mouth of a small stream, 

 half a mile north of Llanaber Church {PL II., Fig. 7). 

 The accompanying diagrammatic section {Fig. 2) will 

 also help to explain it. 



In conclusion, the probable history of this small forest 

 may be interpreted somewhat upon the following lines. 



At some date after the glacial period a tidal flat 

 stretched to the north of where Barmouth now stands, 

 somewhere about a mile wide. This beach is now below 

 low-tide mark, but the alluvial flats mark its position. 

 The daily rise of the tide became blocked by the accumu- 

 lation of a storm-beach, and possibly a range of sandhills 

 to the seaward. Behind this barrier there was left an area 

 into which the Mawddach and other streams would drain, 

 and which was probably flooded by the tides, much as 

 Barmouth estuary is to-day. In this area then accumu- 

 lated a fine silt, the under clay, which deposit was obviously 

 laid down in fairly still water. Gradually the deposit 

 became thicker, covering carcases of the red deer that 

 were floating in the water. As this area was silted up it 

 was colonised by the reeds, which doubtless fringed its 

 borders. After the usual method of colonisation of a 

 swamp, grasses and sedges followed the reeds, slowly 

 building up a soil of sufficient depth to allow a birch scrub 

 to get a foothold. This period of dry land was followed, 

 at any rate locally, by a second and comparatively rapid 

 submergence, for, in some places, Phragmites^ rhizomes 

 and roots are to be found growing in and upon the birch 

 stumps. Accumulation of water behind the storm-beach 

 would be sufficient to account for this, and a rise in the 



