Thornton force is one of the most important
waterfalls of the Yorkshire Dales National Park geologically
speaking of course. Located on the River Twiss, the waterfall
plunges off Carboniferous Great Scar Limestone that was laid down
in a clear sub-tropical sea 330 million years ago.
The water bounces onto rocks belonging to the Lower Ordovician
(Arenig) Ingleton Group laid down some 500 million years ago. The
time gap between the horizontally bedded limestone and the steeply
dipping turbidite sandstones is about 170 million years. Recently
more research on the age of the Ingletonians suggest that they may
be Precambrian after all !
There are dark greenish-grey cobbles lying on the underside of
the limestone outcrop. This is the classic Carboniferous basal
conglomerate that marks an ancient land surface; probably
representative of an early Carboniferous beach. The significance of
this locality was first spotted by John Playfair at the end of the
18th century during his preparation of his book Illustrations of
the Huttonian Theory of the Earth (1802). He described the section
in terms of evidence to prove Hutton's theory that geological
processes of the past were the same as those of today continued
over immense periods of time.
Formation of Thornton Force
Thornton Force was formed in a time when Ordovician
(Precambrian?) mud and sand was deposited into a deep ocean. These
sediments, often of a turbiditic nature, were uplifted and folded
into mountains which were subsequently eroded down over millions of
years. Then the land was submerged beneath a warm shallow
Carboniferous sea. This was then follwed by an uplift of the
Limestone and ice flowing down Kingsdale has further eroded
Kingsdale valley. Further on in time the head of Kingsdale became a
major obstruction to the natural drainage. Thus making the River
Twiss cut a new course in order to bypass the moraine
To log the cache uploed a photo of you/your GPSr with the falls
in the background and e-mail me the answers to the following
questions
1) Estimate the height of the falls.
2) What is the colour of the rock face to the left of the
falls.
Any logs with no photo may be deleted