The Deflated Rock
(previously called The Deflated "ROCK-ON")
Ilkley Moor has an abundance of boulders - large and small. They have naturally eroded over the past millions of years. This rock is quite strange though, as it looks like it has been deflated, or created by a volcano; the applicable technical term is cross-bedding. These effects were caused by erosion by water flowing over the original river bed, and then the force of the last ice age 10,000 years ago which put the largest boulders in place after the glacier ice melted.
HOW THE BOULDERS WERE MADE
Carboniferous rocks comprise nearly all of the solid geology of West Yorkshire, they belong to two main series; the Millstone Grit and the overlying Coal Measures. The hard ‘grit’ sandstones and intervening shale’s of the Millstone Grit outcrop west of Bradford and to the north of Leeds.
These rocks were deposited as sediments in a coastal environment, this is where large river deltas were building out into the shallow tropical marine waters that covered much of Britain at this time. Continuing deposition over the millennia led to the further building out of the deltas and the formation of an extensive low-lying, swampy area in which the succeeding Coal Measures were deposited.
The different rates of erosion in the alternating layers of sandstone and shale’s of the Millstone Grit have created a scarp and vale topography which is responsible for the switchback nature of many of the routes going north from Leeds. The smooth hills and plateau surfaces formed by the Millstone Grit supports extensive but poorly drained pasture land which is prominent in areas such as Ilkley Moor and Wadsworth Moor. The sandstones of the Millstone Grit have eroded slowly to form prominent crags such as those at Otley, Ilkley and Caley (from Natural England, see here).
HOW WE USE MILLSTONE GRIT
As the name suggests it was used for millstones, which you can see carved out in Panorama woods one mile to the east below the Swastika Stone.
5 miles further east at the Cow and Calf rocks, the Bull Rock is now missing, it is the site of the abandoned quarry, the stone was used in the building of the Crescent hotel in the centre of Ilkley.
TO CLAIM THE CACHE
The above link to Natural England may help. Also, as there is no info board at the site, all the required infomaton can be found in the reference section at Ilkley's Victorian-styled library opposite the railway station which is in any case well worth a visit.
1. Post a photo of yourself and your GPSr at the co-ords on the cache page (opional)
2. What is the industrial use of these rocks?
3. Where in a 20-mile radius are the best gritstone formations found?
4. What three elements are found in millstone grit?
5. When were these Carboniferous rocks formed?
6. Evidence of periodic flooding of the delta by the sea is revealed by the presence, usually in the shales, of fossils of coiled shells - what are they called?
7. On the rock you can see groves caused by water. Take a photo of these and your GPSr and post it with your log and/or measure the gaps between the groves and send me the measurements.
Please send you answers by email or GC message. Your log will be deleted if answers are not sent.
See here for more info if required.
FTF goes to Keith aka Two Tykes