Slapton sands could be considered a deceptive name as the beach is actually made from shingle, small pieces of rock eroded by aerial and sub-aerial processes, such as wave action. These particles are then transported around by the waves and deposited adding to beachmaterial. One key process affecting beach size and shape is longshore drift, this happens when waves hit the shore at an angle and will move sediment in a certain direction along a stretch of coastline.
Slate is the bedrock of Start Bay and so is found in the cliffs bordering the beach, it is a metamorphic rock, changed from clays by heat and pressure, but is relatively soft and so erodes easily. You may find large pieces of slate near the cliffs that have recently been eroded but because it breaks down quickly it is hard to spot much slate on the centre of the ridge.
Schist is a very resistant metamorphic rock, and forms Start Point headland jutting out to sea at the south end of Start Bay. It was formed in the Devonian around 395 million years ago. The schist and some of the slate has seams of quartz running through it, quartz is the most abundant mineral in the Earth's crust and you will be able to find plenty of it on the ridge. It is a milky white. You can find some igneous rock on the beach, most transported by rivers that have their source on Dartmoor. Quartzite is pinkish and forms a very smooth pebble. It can be found just offshore and was transported up onto the beach by rising sea levels
Most of the shingle making up the ridge is flint; it makes up about 80% of the material on the beach. Flint is only found about 30-40km offshore from the present day coastline which suggests that Slapton Sands originates from this area.
During the last ice age sea levels dropped dramatically as water was stored in ice sheets, with the coastline much further out than present day a flint beach was formed - with flint being eroded from the sea floor by wave action. As the ice age ended, around 10,000 years ago, sea levels began to rise as melt water from the ice sheets returned to the oceans. The rising sea levels the flint beach landward through a process called roll-over, with beach material being moved from the front of the beach, over the crest and to the rear of the ridge and thus over time the whole beach is moved backward. Around 3,000 years ago the ridge reached the headlands at Strete Gate and Torcross, its current position, but even now Slapton Sands is moving slowly landward.