Collecting Rocks and Fossils |
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These notes are to help our guests enjoy the fabulous geology of the Whitby area safely. The main rocks in the area are sandstones on the top of the cliffs, with black shales underneath. However there are also deposits on the very top from the recent Ice Age. These are mainly clays with lots of small stones in them called ‘erratics’-because they are, er, erratic in the composition. When the cliffs are undercut, all these rocks fall onto the beach and get mixed up; which is why there is so much to find.
The Erratics
Although the rocks underneath are about 180 million years old, the erratics are usually much older. One good item to look out for are pebbles of black limestone with corals in them. These are fairly common and were eroded from Carboniferous Limestone that is over 300 million years old. There are also various granites and other rocks. Their age may run into billions of years, but the main thing is that many of them are very attractive and great fun to sort through.
The Sandstones
These beds formed in a delta at the mouth of a large river. They contain lots of ironstone which weathers bright red with many intricate structures. There are plenty of plant fossils as well, which are turned to black coal and so stand out easily to the hunter.
The Shales
These rocks contain ammonites, belemnites, plesiosaurs, wood and rarer things such as lobsters and even pterodactyls. The Jet Rock beds in the middle contain seams of Whitby’s famous jet, which is really an unusual form of coal. All of this area was swamps and lagoons with only a little fine sediment. The fossils are so varied because periodically tsunami waves would wash huge quantities of marine life into this shallow water. As there was too much for other animals to eat them and it was too boggy for large carnivores, a lot of this life became fossilised.
Collecting
As will be shown below, cliffs can be dangerous, so hacking fossils out of them is dangerous, as well as very hard work. However, we have the sea to do the work for us. When banks of shingle form; the sea sorts out the pebbles into different sizes. The ammonites are in nodules 2-4” across usually, and so you look for them where most of the pebbles are this size. You can often see the serrated edge where the shell is weathering out. Jet is much lighter and tends to be at the top of the shingle. Erratics are all sizes, so it is a bit more hit and miss, but then there are lots of them.
Tools are a problem for many. Only proper geological hammers are safe, other types of hammer may shatter. Bits of nodules have been blinding collectors for centuries, so goggles are a must. Better still, take your nodules home and get a friendly builder to split them. If you do split something-and some types break quite easily-then bind the two halves together with masking tape to keep them together and stop them getting scratched. Fossils should be washed and dried carefully to get rid of any salt and then varnished with thinned lacquer to preserve them. Pebbles can be treated the same way, but it is important not to overdo it.
You are unlikely to find a great big beastie, but there are some marvellous ones in the town museum. What is possible to find are individual vertebrae, usually a couple of inches across. They are quite like our own backs, so it is possible you are turning up bits of a very ancient ancestor.
Safety
Collecting is great fun, so is diving and swimming, but like all outdoor activities it needs a bit of thought and preparation to do it in complete safety.
Equipment
As stated above, use only proper hammers or a hammer and chisel. Use goggles-and gloves if your hands are not used to rough work. Good footwear and clothes in bad weather, but ordinary boots do not help on slippery green rocks.
Cliffs
Shale cliffs are impossible to climb safety and you should keep off them. You can often see or even here small flakes of shale coming down. When enough small pieces have fallen, a larger nodule may follow with potentially lethal consequences. When you venture near a cliff, look up and see if there is a hangover or any loose blocks. Keep your ears open and run down the beach at the slightest sound from above-common sense really.
Tides
The tides at Whitby rise up to 6 metres and can be very dangerous, especially when the sea is an easterly. Always consult tide tables, or look on the board at the swing bridge, to find the high water times. With large breakers and a strong wind off the sea, the tide may not go out as far as predicted and then come rushing in. The best way is to go onto a beach as soon as possible after high water. The time you get on before low water is the time you can come off after low water, but only on a calm day. Usually this leaves 4-6 hours collecting time, which is ample for most people. Some beaches such as Runswick Bay and Port Mulgrave are a lot safer in all but the worst conditions. When in doubt ask the locals-almost everybody in the district is keen to avoid tragedies and glad to help. NB. Being a good swimmer is not much use if a tide pulls you out.
