On land, water moves sediment of all shapes and sizes, and rivers are the main arteries of this transport network. River deposits are often dominated by gravel, sand, clay and mud. The unidirectional currents of rivers produce a variety of sedimentary structures such as: ripples, cross-bedding, load casts, grading, braiding, laminae and these features can easily be identified in many of the sedimentary rocks on Arran.

When studying fluvial and deltaic rocks one can deduce the direction of flow of the rivers that laid down the sediment: the palaeoflow. Using the nature and orientation of the structures in the rocks, as well as fossils and the texture of the sediment itself, one can deduce exactly which type of river system existed; whether it be a gently meandering river, an alluvial fan, the headwaters of a river or a braided river system. So while rivers such as the Clyde (shown on right with an impression of the new Science Centre) may move and change over geological time periods, their former presence can be deduced from the characteristic sediments that they deposit. As rivers flow from mountains into flat-lying areas they loose energy and deposit the sediment they were carrying - the lower the energy level, the finer the sediments being carried and deposited.

Fluvial deposits characterize the Old Red Sandstone on Arran. These conglomerates and sandstones were deposited by large rivers carrying sediment that was being eroded from the rapidly rising Caledonides. The wet climate helped to produce flash floods which in turn produced the coarse conglomerates of the type seen in Sannox Burn.

The Carboniferous was a time of tropical weather for Arran. The fluvial and deltaic deposits of this period can be seen at Corrie. The sedimentary rocks are rich in fossils and consist mainly of channel and crevasse splay sandstones interbedded with overbank silts and muds. The rivers drained into large delta systems which were often adjacent to swampy areas full of giant fern trees. The accumulation of plant material in these swamps eventually led to the development of the coal that characterizes the Carboniferous. Coal on Arran can be seen only at Laggan.