Ogmore-by-Sea (Welsh: Aberogwr, meaning "Mouth of the River Ogmore") is a seaside village in St Brides Major community in the Vale of Glamorgan, Wales.

Many ships, in particular, were destroyed on Tusker Rock, a brutal reef slightly out to sea that is totally covered at high tide.

They are all sedimentary rocks, originally deposited as lime, mud, sand and coarse pebbles, and over long periods of time these were compacted and solidified into limestone, shale and conglomerate.

Deposition resumed during the Triassic Period when the area was a desert with hills of limestone, and a dry plain where the Bristol Channel is now.

Short violent storms caused flash-floods which carried debris down the hillsides and deposited it as alluvial fans of coarse, red conglomerate at the edge of the plain.

About 205 million years ago, at the beginning of the Jurassic Period, the sea began to drown the land and the limestone hills became islands before finally being submerged.

After the early Jurassic no evidence of geological events is preserved until the end of the last ice age, about 10,000 years ago.