The opening, in the summer of 1858, of a hard stone quarry in the search of a durable stone suitable for the construction of the new naval dock brought about the discovery of a bone-cave containing the remains of hippopotamus and other animals, near the Phoenician remains at Crendi. Mr. Horner reported this in his presidential address to the Geological Society in 1861, consequently adopting the name of Qrendi for this quarry and cavern in his notice of this interesting discovery.
On the demise of Mr. Horner, Dr Leith Adams M.B., F.G.S., F.R.S, who arrived in Malta two years subsequent to the first discovery was entrusted with the investigation of this interesting and important find. His more recent labors amongst the debris enabled him to procure similar remains and to learn the history of the cavern from the quarrymen. Reports were later submitted to the Royal Dublin Society Journal and the British Association Geologist Society. Throughout his investigations, several additional caverns were located and excavated.
Bones of extinct animals are fairly abundant in Malta, and many paleontologists have made these islands their hunting ground. Renown experts in this field included Spratt, Busk, Parker, Falconier, Lieth-Adams, Issel, Caruana, Cook, Tagliaferro, names which will always be connected with the Paleontology of Malta. The animals discovered include elephants, swans, and hippopotami, none of which could thrive far from a rich vegetation and a large expanse of water. According to Profs. Hull and others, the Mediterranean Sea was once a series of fresh water lakes connected with one another by channels, and with land passages from Europe to Africa at the strait of Gibraltar, Sicily, Malta and Egypt. Along these passages, the early pachyderms and ruminants traveled southwards to North Africa when they were driven by the increasing glaciations of Europe.
The remains of those animals that tarried on the Maltese bridge were in the course of time, washed into fissures, caves and ravines where, fossilized by the action of soil and water, they have been discovered in a more or less perfect condition. The Maghlaq Cave No. 3 was also discovered in 1858, and consisted of a cavern opening horizontally containing the remains of Hippopotamus pentlandi together with a solitary molar of one of the elephants. Although a considerable amount of the fossilized remains were found in a damaged state, the same cannot be said about the remains of Hippopotamus pentlandi and Hippopotamus minutus that were otherwise found in a perfect condition. Discovered within the same cave were remains of Myoxus melitensis, bird bones and entire recent land-shells.
Dr Leith Adams also discovered the Mnajdra Gap Cave No 6 in 1863. Just a few meters from the Maghlaq cave No 3. Within this cave portions (apparently entire skeletons) of elephants in conjunction with enormous quantities of the bones of Myoxus melitensis and of large aquatic birds including Cygnus falconeri. Fragments of chelonians with recent land-shells belonging to Helix, clausilia and bulinus were also found.
In the middle Maghlaq Cave No 5 located a few meters distance from the
Maghlaq Cave No 3 remains of Myroxus melitensis together with teeth of
arvicola besides bones of large birds, small frogs and recent land shells
were discovered. Dr Adams further reports in 1863, of the discovery of
the remains of the largest forms of elephant. A much mutilated skull with
penultimate true molars was found within the Maghlaq Fault (No 7) Cave
Work on the Mnajdra Gap cave was recommenced early in December 1865 at
a point where work had previously terminated. This section of the cave
with its largest length in access of 30 meters with a maximum width of
between four and fifteen meters was covered with parent rock and structure
and stalactite. Fossilized remains were found in greater abundance and
in the best state of preservation, teeth and tusks of elephants, the remains
of the large dormouse and land-shells were found through out the cavern.
Remains of birds were also very common not only in this cave but also
in all the localities. Foot and wing bones represented raptors of large
dimensions from Mnajdra Gap where likewise water birds including Gigantic
Grallae and anseres were plentiful. The presence of a very large river-tortoise
was repetitively by the discovery of heads of femurs and other portion
of the skeleton.