Part 05: and so to the present day.....
The landscape has continued to develop during the last 10,000 years of the post-glacial or Holocene period. There has been a gradual colonisation by vegetation co-eval with the development of soils - there is a classic chicken & egg situation here, did thesoil control the plantsthat grew or did the plants alter the soil to suit themselves? In reality, abit of both!
Melting ice across the northern hemisphere led to progressively drowning of the land as sea level rose, constantly changing the shape of Anglesey. At the height of the Ice Age, the Irish Sea basin was completely dry, glacial deposits spread out across the sea floor. Plants colonised this area forming dense forests, traversed by meandering rivers. Rising seas drowned these lands and eroded the glacial deposits, winnowing out sand to be driven landwards by the waves to form exentsive sandy beaches from which prevailing winds blew the sand into impressive sand dunes. Although the broad outline of Anglesey can traced back to Permo-Triassic times [i.e. the rocky outline], the soft sedimentary features we see today are largely develoepd during this time, and are continuing to change to the present day.
GeoMon scientists have produced a leaflet explaining some of the soil types to be seen around the coastline, whilst not a typical way to study the soils of an area, it provides a very 'easy to see' account of some of our soils without the trouble of digging soil pits.
Soil is formed when environemntal factors, climate and vegetation get to work altering the surface geological material according to its position in the landscape; over time they bring about changes in the chemical and phsyical make up of the material to form soil.
As we have seen, Anglesey has a very diverse geology and an extensive range of soft sedimetns, glacial boulder clay, fluvioglacial sands and gravels, river silts, wind blown sand and marine alluvium. The climate hardly varies, but the diverse geology does affect the type of plants able to grow which in turn begin to alter the soil. Landscape is fairly subdued, with only a few small hills and very few, small rivers, but the hydrology is very varied due to varying permeablity of solid rock, boulder clay and sand. Hence there is a very diverse range of soil types - leading to a diverse range of plant habitats.
Above: that part of the geological time-scale from the end of the Mesozoic (the "K-T Boundary"), 65 million years ago, up to the present day, consisting of one era - the Cenozoic - which is subdivided into two periods, and then into epochs, such as "Eocene". The current epoch, the Holocene, began only 0.01178 million years ago, so that it is too small to show up on the chart. The Quaternary consists of the Pleistocene and Holocene lumped together. Graphic: John Mason.
Above: an early Cenozoic dyke cutting older rocks on the coast at Porth Namarch, near Holyhead. Basic in composition, with a lot of iron-bearing silicates, the dyke-rock shows the distinctive, spheroidal "onion-skin" weathering pattern.
Photo: Stewart Campbell.
Above: till - deposited by the Irish Sea ice-sheet, about 20,000 years ago - is now being reworked by the sea at Beaumaris - part of the seemingly endless cycle of sedimentary erosion and deposition.
Photo: Stewart Campbell.