Seashells, seashells... in the bedrock

The Maltese islands are made up of different layers of sedimentary rock. In geological terms, the islands are very young. They were created long after dinosaurs became extinct and so it is impossible to find dinosaur fossils in any of the islands’ rocks.

The fossils found locally are mainly of marine organisms. The species of these organisms, however, change according to the layer in which they are found.Fossils are the preserved remains of plants and animals or their traces. They provide palaeontologists with important information about both the geology and biology of the earth. An object is considered a fossil if it is older than a certain minimum age, which for most palaeontologists is 10,000 years. The oldest fossils are about 3.4 billion years old.

The oldest layer, the lower coralline limestone, is made up mainly of reef-forming organisms such as calcareous algae and coral, where one is more likely to find bivalve seashells. At the very top of the lower coralline limestone layer is a shallow but very concentrated layer of large flat sea urchins.

The globigerina limestone layer is made up of the remains of planktonic organisms. Some parts of this layer are rich in fossils of free-swimming organisms such as scallops as well as bottom-living creatures such as sea urchins and crustaceans.

Blue clay was formed from a sediment that originated on land, probably from eroding landmasses to the north that were being uplifted as a result of tectonic action. Fossils in this layer are few, and are mainly molluscs and coral.

The penultimate layer, the greensand, is absent in many parts of Malta but forms a thin layer in many parts of Gozo. Greensand is characterised by its orange-brown colour (green before being exposed to air) and large amount of fossils.

The most obvious fossils belong to large sea urchins but fossilised fish have also been found in some places. The topmost layer, the upper coralline limestone, which was the last layer to form, is similar to the oldest layer, the lower coralline limestone.

This article was published in The Times on 3 April 2013.

The ecological importance of Il-Maqluba

Il-Maqluba is a site of natural and geological interest on the outskirts of the small village of Qrendi. It is a circular crater known as a sink hole that was formed when the roof of a large underground cave collapsed. 

It is believed that this happened in November of 1343. In geological terms this is a very recent event and no major changes have taken place since the event occurred. Given that caves are common in the Maltese island it is not surprising to find such a structure and in fact other similar structures of varying ages can be found. 

Sink holes slowly fill up with sediment that is blown or washed into it and eventually it fills up completely to form a soil-filled depression. Such a structure is found near St Martin’s Church at Baħrija and it is now a very good area for agriculture. Along the west coast of Gozo one can also find similar structures one of which is known as the Inland Sea.

Caves form when acidic rain water flows through hollows and fissures dissolving the rock and creating tunnels which eventually, as a result of more and more water flowing through them, widen and enlarge and eventually become caves.

The best known cave is Għar Dalam near Birżebbuġia which when excavated yielded thousands of fossilised bones and teeth of long extinct animals including dwarf elephants, hippopotamus and deer.

Il-Maqluba is important ecologically because in it one can find several interesting species of plants and animals which thrive in it because of its inaccessibility. Amongst these one finds several large specimens of Malta’s national tree - the sandarac gum trees (għargħar) which grow on the cliff sides. 

Until about a couple of decade ago it was believed that these were the only specimens of this tree, which is a native of North Africa, which were still growing wild in the Maltese islands. The site is also important because on its walls one can find a population of the Maltese salt-tree (xebb). A species of slug which is endemic to the Maltese islands was found in the depression together with other species of rare animals including ants and a silverfish.

It is not surprising that such an unusual structure needed an explanation that could be understood by the local people. They thus came up with the story that in ancient times at Il-Maqluba there was a small village inhabited by evil people. 

One day the land collapsed and the whole village was swallowed by the land. All the inhabitants died except for a pious lady who was praying in the small chapel next to the village. In fact there is an old chapel dedicated to St Mathew still standing next to the depression. 

This article was published in The Times on 10.02.2010