Hookney Tor is a windswept rocky outcrop on Dartmoor at 414m / 1358ft ASL. It watches over the Grimspound, an intriguing bronze-age circular enclosure with the remains of 24 houses, some inhabited until medieval times. It will have a post in its own right in due course. We investigated both with our granddaughter Berry last August during a short holiday together (grandparental treat!) on Dartmoor.
After exploring the Grimspound, there is no doubt about the next achievement to tackle: a steep stony path leads invitingly from the walls to the top of the Tor. As you climb, the Grimspound quickly gets smaller below you.
Berry was not the only wild creature on the moor…
AN EXCITING DISCOVERY THAT WAS DISAPPOINTING
As we climbed, we noticed that the rocks all around were embedded with fossils. Or so we believed. We took lots of photos of these amazing calcified creatures that by some strange process were to be found at nearly 1500ft. Only later, when we did a bit of research online, did we find out the disappointing truth: not fossils, but megacrysts. The technical explanation is as follows:
The main exposure at the Tor is of megacryst granite (also known as “Giant Granite” or “Big-Feldspar Granite”). It is probably from near the roof area of the batholith. The feldpars are of perthitic orthoclase that is porphyroblastic (later replacive crystals) in origin and not phenocrysts (large crystals that have developed in the magma). In some places the southwest England granite megacrysts have been seen to develop into aplite (fine-grained quartz-feldpar veins of late origin), which is possible for porphyroblasts (developing by replacement after the veins) but not for phenocrysts (early and which should be cut through by the veins).
A DISAPPOINTING DISCOVERY THAT WAS EXCITING
Tupperware at nearly 1500ft? The plastic rubbish left behind by some idle picnicker? But no… Berry spent some time exploring the crannies of the rockiest outcrops, and in the process made her next ‘Letterbox’ discovery… [The previous year’s find is HERE]
Berry was not the first person to discover the box, which had been left by a girl from Surrey, with a message encouraging people to write in the notebook inside. This was already well-filled with the names, addresses, messages and drawings of previous explorers. There was also a strange mix of ‘souvenir’ items people had left – a car park ticket from Alton Towers, a ‘poppy day’ poppy, a couple of smoothed-out sweet wrappers, a button, and other such debris that walkers might find in their pockets… So Berry added a 1p coin, and added her contribution to the notebook. It may not have been an official Dartmoor Letterbox, but it was a lovely idea to have hidden it for others to enjoy.
Credit: photos 4, 5, first megacryst, and all agile activity by Berry