North
Yorkshire has an interesting and changeable geographic
history. Generally the geology of North Yorkshire comprises
of sedimentary rocks which slope gently to the east leaving
the oldest rocks present in the west of the County and the
youngest in the east.
The North York Moors dominate North-east Yorkshire where the
Hambleton Hills and North Yorkshire Moors rise abruptly out
of the earth to the east of Thirsk. This whole area mainly
comprises of mudstone and sandstones of Jurassic age. The
porous sandstones give rise to the free-draining soils that
support the heathland vegetation of the North Yorkshire
Moors. These marine and delta deposited rocks are superbly
exposed on the Yorkshire coast from Staithes to Filey and
you can find many fantastic fossils falling out the rock
face.
• Lower Jurassic Shales, clays and thin limestones
and sandstones were deposited in a shallow sea at the
beginning of the Jurassic era.
• Middle Jurassic during this time the moors
experience a period of gradual uplift resulting in mudstone
and sandstone being deposited on a low lying coastal plain
crossed by large rivers.
• Upper Jurassic at the end of the Jurassic era the
land once again began to sink beneath the sea. At first the
sea was shallow and calcareous sandstones and limestones
were deposited.
Subsequently, about 30 million years ago, the land was
uplifted and tilted towards the south by earth movements.
The upper layers of rock were eroded away and the older
rocks were exposed in places. Because of the tilt the oldest
rocks became exposed in the north.
Approximately 20,000 years
ago the the most recent glaciation, the Devensian, ended. As the
climate warmed up at the end of the ice age the snowfields on
the moors began to melt. The resulting meltwater was unable to
escape eastwards, westward or northwards because it was blocked
by ice. This meant Huge torrents of water were forced south from
the Esk valley flowing southwards gouging out the deep
Newtondale valley as it went. In the area of the Vale of
Pickering water from the moors formed a vast lake. After a while
this lake filled its basin and then overflowed at the lowest
point which was at Kirkham. Here it cut the steep sided Kirkham
gorge. When the glacier finally retreated they left deep
deposits of boulder clay and glacial alluvium behind.