The Leaving of Ice
The ice sheet began to recede around 16,000 years ago and Scotland was largely free of ice by 13,000 years ago. Between 13,000 and 12,000 years ago the weather was like today, but warmer in summer and cooler in winter. As the ice melted local sea level was high flooding the lower parts of the Forth and Clyde valleys and Loch Lomond. Where ice retreat slowed, for example in the Kincardine Bridge area and around Stirling, large deltas and terraces built out into the sea. Relics of these features can still be seen around Falkirk and Stirling. Marine sediments are found at 40 to 45 metres above sea level east of Stirling. Conditions were still arctic in the winters, as shown by the fossils found in the marine clays laid down during this period. Following removal of the ice, the land rose and by 11,000 years ago sea levels dropped to below present level. These rapidly changing sea levels left a series of raised beach features that can still be recognised in places.
The Loch Lomond Re-advance
The climate deteriorated and between 11,000 and 10,000 years ago arctic conditions prevailed. Ice built up in the Southwest Highlands and advanced once more into the Lowlands. This Loch Lomond Re-advance is well documented, with the related landscape features and deposits being little altered in many areas. Ice reached Callander, the Lake of Menteith, Drymen and Alexandria.
The Holocene Stage
About 10,000 years ago the weather began to get gradually warmer up to around 6,500 years ago. Woodland developed until about 5,000 years ago when man started to remove it. At first after the ice had gone, rising land levels again competed with the overall rising sea level, but the lover Forth and Clyde valleys were eventually flooded to a level of some 16 metres above current sea level at about 6,500 years ago. The position of the shoreline which existed at this time can be recognised from east of Grangemouth to Aberfoyle, and also in the lower Clyde valley.
In the enlarged Forth estuary peat began to develop soon after the ice had gone but was stopped by the rising sea level and grey tidal Carse clays and silts were widely deposited. Peat continued to form locally on Flanders Moss where coastal bogs persisted. Only sands and gravels and peat deposits were laid down in the Clyde valley. The sea entered Loch Lomond for two short periods before 6,800 years ago, after which it remained a sea loch until 5,500 years ago. The falls in sea level and the warmer, wetter weather since the last glaciation have seen the formation of river and stream gorges and waterfalls such as the Falls of Leny.
Landform development continues to this day. Rivers continued to develop their floodplains during the Holocene and slopes readjusted to post glacial conditions. In the unconsolidated sediments on the low-angled valley floors, river meander belts developed, as along the Endrick Water and River Forth. The meanders on the Endrick, near to where it enters Loch Lomond, are still actively migrating across the floodplain as banks erode. The reworking of the floodplain sediments and the long history of changes in the river course are clearly seen in the old channels and cutoffs abandoned on the floodplain.