The stone which is composed of Old Red Sandstone measures 3.7 m (12 ft) high by 2.8 m (9 ft) wide by 0.6 m (2 ft).
The hill is formed from mudstones of the St Maughans Formation of the Old Red Sandstone laid down in the Devonian period.
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A slab of Old Red Sandstone, the cross slab was discovered in the late 18th century, having been reused as paving in Fordoun Parish Church.
The hill has not eroded as fast as the surrounding limestone as it is made of Old Red Sandstone deposited in the Devonian period approximately 400 million years ago.
It is perhaps the most significant of all of the calcretes which occur within the uppermost Silurian and lower Devonian sequence of rocks which constitute the Old Red Sandstone of the Anglo-Welsh Basin.
Wales' many fine cathedrals, abbeys and castles have used a variety of stones in their construction; Caerbwdi Sandstone in St David's Cathedral, Old Red Sandstone at Llanthony Priory and Tintern Abbey, 'Blue Pennant' sandstone in Caerphilly Castle and Sudbrook Sandstone at Caldicot Castle to name but a few.
Then he obtained a copy of Hugh Miller's Old Red Sandstone (published in 1841), and he began systematically collecting with hammer and chisel the fossils from the Caithness flags.
In 1858 he edited an edition of Hugh Miller's Cruise of the "Betsey." He was the author of numerous essays on the geology of the Malvern country, notably of a paper "On the passage-beds from the Upper Silurian rocks into the Lower Old Red Sandstone at Ledbury" (Quart. Journ. Geol. Soc. 1860).