94 LIVERPOOL BIOLOGICAL SOCIETY. 
accumulated the Lavan Sands. During this period the 
ordinary denuding agents gave the finishing touches to 
the scenery of the district, supplementing the volcanoes 
that had built up the mountains, and the glaciers that had 
eroded the valleys. 
In conclusion, therefore, let us glance at the splendid 
geological panorama to be seen from the south-west end 
of the island, by the old flagstaff. To the east may be 
seen the limestone massif of Great Ormes Head, once 
united to Puffin Island, and thus to the bare undulating 
limestone hills of Anglesey that bound the horizon to the 
west. Southwards, beyond the Lavan Sands, towers the 
quarry-terraced cliffs of the bronzite felsite of Penmaen- 
mawr, to the west of which extend the heather covered 
gullied slopes of the lower Silurian rocks that form the 
Caernarvonshire range. Still further westward, behind 
the town of Bangor, can be seen the old ridge whose age 
has been so keenly contested by Ramsay, Hughes, Hicks, 
Bonney, Roberts, and many more. Beyond can be seen 
the mass of lavas and volcanic ash that form the peak of 
Snowdon. This view affords an admirable summary of 
the past history of the district from the old Twt Hill to 
Bangor ridge, the Cambrian of Anglesey, the lavas of the 
lower Silurian, and the limestone of the Carboniferous, to 
the glacial drifts that line the shore, and the still accumu- 
lating sandbanks that will silt up the Menai Straits, just 
as a neighbouring estuary within no distant date has 
given place to the fertile meadows of Malldraeth Marsh. 
