the upper Findhorn is largely made up of the Grampian Division of the Moine Supergroup, a formation that stretched from south of Forres to Lochindorb and beyond. These rocks are typically metamorphosed sediments of sandstone that are rich in quartz mixed with some shale and mudstone that date from circa 750 mya. The schists that underlay the Streens in the middle reaches of the Findhorn were once thought to be part of the younger Dalriadan Supergroup but are now considered to be Moinian as well. The Grampian Slide is a zone of shearing between the younger Grampian Division and the older Central Highland Division. In the lower Findhorn the bedrock is Old Red Sandstone that was deposited after the Caledonian orogeny. The rapid uplift of the mountain terrain to the south was accompanied by similarly rapid river erosion that resulted in sediment being spread throughout the Moray Firth basin and further north to Orkney and Shetland some 360–400 mya. At this time the land lay some 20 degrees south of the equator and experienced a semi-arid climate. During the Tertiary period some 65–50 mya volcanic activity on what is now the west coast of Scotland resulted in considerable uplift there and the creation of the slope that dips in an easterly direction that the modern Findhorn river follows. With the onset of Pleistocene glacial period some 2 mya the whole of northern Scotland became ice-bound. For example, the Cairngorm mountains immediately to the south of the Findhorn valley became covered in ice some thick. The melting of the ice, which occurred comparatively rapidly, resulted in "vast volumes of meltwater" creating further erosional and depositional features, such as river terraces in the middle reaches of the Findhorn and moraines such as the Cluny hills downstream. The great weight of the ice depressed the land surface and with the end of the glacial period there resulted both sea level rises and isostatic rebound of the land which combined with periodic uplifts resulted in a complex interplay of land and sea with a prominent raised shoreline between Nairn and Forres that skirts the Culbin Forest. However, the shores have not been static even in historic times. The earliest detailed map of the Findhorn estuary dates from 1590 and was made by Timothy Pont. It shows a long sand bar stretching west from the site of the village of Findhorn along the Culbin shore.