Maroon Town

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Apr 5, 2004

RUDIST ROCK CAVE


Position: Flamstead, St James. (GPS position reserved due to paleo).

Field notes: GUY VAN RENTERGEM

Cavers: G. van Rentergem, R. S. Stewart, B. Murray, D. Roeber

Time in: 12:00 EST, Time out: 13:45 EST

THREAT VULNERABILITY: Intermediate

Monday, April 5, 2004, on our to-do list: Rudist Rock Cave. Although a small cave, it made a big impression on me.

The cave got this strange name because of the presence of Rudist fossils. I had only seen the name once before, in the excellent work, "Jamaica, A Geological Portrait", by Anthony R.D. Porter. In chapter nine, the author talks about the Barrettia - a fossil shell discovered in Jamaica. This fossil was found for the first time by Lucas Barrett, in the early 1860's, in the district of the Rio Grande. The fossil was later catalogued as a member of the Rudists group. This is a rather neglected group of strange bivalved molluscs that lived during the Cretaceous Period, from 140 - 65 million years ago. The valves of the shells are nearly always highly asymmetric, and they are considered to be reef builders. They seem to be typical for tropical deposits, so my interest was awakened. During my previous visits to Jamaica, I had never encountered any fossils; the possibility to see some original Jamaican fossils was more than welcome.

Today, it is Monday, and the number of available team members is again seriously reduced. Fortunately, we have reinforcements from the Peace Corps. Our group counted four souls: Stef, Brian and his wife Dana, and I. The usual long drive over bad roads for some hours took us to the Maroon Town district. This time, the location mentioned in Jamaica Underground was correct, and in no time we had found the cave.

Rudist Rock Cave is located in a small rock outcrop at the edge of a shallow depression. The environment is deforested and is now used as pasture. The entrance looks a bit like that of Roehampton School Cave. On the outside, there is no real sign of a riverbed, so the cave is a kind of window on an underground river. A small horizontal passage meanders into the hill with only a trickle of water flowing through it, but everywhere, like in most river caves, there was dirt and plastic. I really don't want to be in this cave when it starts raining; the friendly trickle will change into a roaring monster.

In the pools of water, we saw the usual crabs. Their bodies measure 3 cm and have a dark brown colour. The legs are wide and stretch about 15 cm. A bit stranger was the purple mould we saw in different places. The cave wasn't difficult, and only in some places was a crawl necessary.

The first hundred meters were a disappointment for me because no fossils were seen. Then, we saw the first one, a strange round structure about 20 cm in diameter. I recognized it immediately as a member of the Rudist family. As we went deeper into the cave, more fossils were seen in the massive rock of the cave walls. Indeed, this is Rudist country.

The "normal" cave ends at a small horizontal rift. Flat on my belly, I went on. After 8 meters, there is a crossroads which turns back after some metres. Then, it becomes wider again with deeper water, but it eventually ends in a small passage between the boulders. With some effort, it would be possible to go on. From this point, I collected a Rudist that is now displayed at the Last Resort, in Windsor.

On our way back, I made a rather remarkable discovery. In a low passage, where we had to go through the river on our hands and knees, I saw it glistening between the pebbles... a sea urchin with a diameter of 3 cm! It looked so good and fresh, I at first thought it was recent, but then it hit me; we were about 500 m above sea level and deep into the Cockpit Country! I turned it upside down and saw the interior of the sea urchin filled with hard rock. This fossil appears to have eroded out of its rock matrix, and was now lying in the riverbed. It is difficult to tell where it came from. Was it washed from the outside into the cave or was it eroded from the walls of the cave? My guess is that it was eroded from the cave walls.

This cave is fascinating enough to visit again, to try to push the known borders further. The existing map, available from Jamaica Underground, is too basic and lacks detail. A resurvey of the cave must be considered.

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