VICE ADMIRAL T. A. B. SPRATT RN (1811-1888)
Vice Admiral T. A. B. Spratt RN (1811-1888)
Capt. Thomas Spratt (later Vice Admiral) was the first to provide a clear geological description of the Maltese bedrock during his stay in Malta while serving on the naval vessel HMS Beacon (1836-1846). His description of the bedrock formations appeared in his 1843 publication “On the Geology of the Maltese Islands” in the Proceedings of the Geological Society of London. He described the Maltese rocks to be of Miocene age and subdivided them into four groups on the basis of their mineral and fossil contents. He called these groups: Coral Limestone, Marl, Calcareous sandstone and Semi-crystalline limestone. He also subdivided the Coral Limestone into two beds and the Calcareous sandstone into five beds that included the phosphatic nodule beds.
Spratt’s publication included a topographical map showing some faults and four inset geological cross-sections. However it did not show any mapping of lithology. A second edition of his work was published in 1852 “Geology of Malta and Gozo” and in 1854 Sir William Reid, then Governor of Malta, reprinted the edition. In a report of the Curator of the Geological Society of London attached to the reprint it was noted that a geological map of the Island of Malta, made by the Right Hon. Earl of Ducie, was about to be published (see below).
Spratt’s publication “On the Geology of the Maltese Islands” 1843
DR ANDREW LEITH ADAMS FRSE, FRS (1827-1882)
Dr Andrew Leith Adams
Dr Adams was a Scottish physician, naturalist and geologist who served as a physician in the British army and was stationed in Malta for six years. He spent his spare time studying the geology of the Islands and expanded on the work of Spratt. He took up the structural work started by Spratt and discovered the Magħlaq Fault in 1861. He described the Miocene beds and modified the version of Spratt’s subdivision by dividing the strata into five groups rather than four: Upper Limestone, Sand Bed, Marl, Calcareous Sandstone, and Lower Limestone, a subdivision of five that survives to this day. He also subdivided the Upper Limestone into three parts. He published his works in 1864 in “Outline of the geology of the Maltese Islands” and in 1870 in “Notes of a Naturalist in the Nile Valley and Malta”. To the latter publication was attached a geological map prepared by Hon. Earl of Ducie using Adam’s fivefold subdivision of the bedrock.
RIGHT HON. EARL OF DUCIE
Geological Map prepared by Hon. Earl of Ducie
Adam’s revised classification of the Maltese rocks was used by the Right Hon. Earl of Ducie in surveying the Islands and constructing a geological map during a stay in Malta in the winter of 1852-1853. The new map, entitled “Geological Map of the Maltese Islands showing the Surface Rocks and Faults”, was printed in 1854 by W. & A. K. Johnston of Edinburgh and attached to an 1870 publication of Adams entitled “Notes of a Naturalist in the Nile Valley and MaIta”. This was the first complete geological map showing both the structure and the lithology of the Islands.
SIR JOHN MURRAY (1841-1914)
Sir John Murray
In 1890 Sir John Murray, oceanographer of the Challenger Expedition, published a paper in the Scottish Geographical Magazine entitled “The Maltese Islands with special reference to the Geological Structure” in which he collected together the previous works of others and added his. The current terminology of the five formations of the Islands dates back to this work. He also appended a comprehensive geological map printed by the British cartographer John George Bartholomew of John Bartholomew Co. in Edinburgh on reduced 2 inches to the mile Ordinance and Admiralty Surveys of 1824.
Publication of the Ordinance Survey 1890
The map was based on geological data from surveys by the Right Hon. Earl of Ducie, Capt. T. A. B. Spratt, Dr. Leith Adams and Dr. John Murray himself. It depicted the five formations with the terminology established by Murray, alluvial deposits and the faults more or less as we know them today. It also included an inset geological section across Gozo, Comino and Malta, three inset views of the coasts with superimposed coloured strata, and an inset sketch map of the bathymetry surrounding the Islands.
BRITISH PETROLEUM EXPLORATION CO. LTD
In 1954 D’Arcy Exploration Company (later BP Exploration Co. Ltd) was awarded a petroleum exploration licence onshore Malta. In preparation of drilling a deep exploration well on the Island the company drilled three stratigraphic wells and undertook a geological survey by K. C. Dunham, M.R. House and A. A. Wilson. A geological map was prepared on the basis of the survey and published by the Ordinance Survey in 1955 at a scale of 2 inches to the mile.
BP Geological Map of Malta (1955)
DR H. M. PEDLEY
Since the publications of Murray’s and BP’s maps, several authors contributed further to the structural and lithostratigraphical understanding of the bedrock geology of the Islands. Of these, the contributions of Dr. H. M. Pedley remain the most outstanding. In 1974 he published his landmark work on the solution subsidence structures of the Islands. In 1971-1975 he carried out a geological survey of the Islands at 6 inches to the mile and in 1976 he published small scale maps jointly with M. R. House and B. Waugh. In 1978 he improved the detailed understanding of both lithostratigraphy and palaeoenvironmental within the two Coralline Limestone Formations.
OIL EXPLORATION DIRECTORATE
Dr H. M. Pedley resurveyed the Islands again in 1992 at a scale of 1:25,000. These surveys were revised by the Oil Exploration Directorate and formed the basis for the publication of the geological map by the Oil Exploration Directorate, Office of the Prime Minister in 1993. The map was printed in two sheets by the British Geological Survey (C. Simpson, cartographer). It depicts the structure and lithology at member level and includes a correlation chart, three geological sections, a sketch of the solution subsidence structures in Gozo, and descriptions of the members.
CONTINENTAL SHELF DEPARTMENT
In 2016, the 1993 geological map was digitised by the Continental Shelf Department using Geographic Information Systems (GIS) technology. The entire geological information was organised under 6 themes/layers: quaternary, tertiary, stratigraphical boundaries, bedding, faults and solution subsidence structures.
Digital Map (based on 1993 Geological Map)
CONTINENTAL SHELF DEPARTMENT AND THE BRITISH GEOLOGICAL SURVEY
The 1993 geological map was resurveyed at a scale of 1:10,000 by the British Geological Survey in 2021-2022 through a contract awarded by the Continental Shelf Department. The resurveyed map was published by the Department in 2022. The entire geological information is now organised under 7 themes/layers: bedrock geology, superficial geology, artificial geology, fault features, fold features, solution subsidence features and bedding measurements.
The theme layers are available for free download in Shapefile format from this website. It is also possible to visualise and explore the data through the Web GIS Map.
REFERENCES
Adams, A.L., 1864. Outline of the geology of the Maltese Islands. Ann. Mag. Nat. Hist., ser. 3, 14, 1-11.
Adams, A.L., 1870. Notes of a Naturalist in the Nile Valley and Malta. Edinburgh.
Murray, J., 1890. The Maltese Islands with special reference to their geological structure. Scott. Geogr. Mag., 6, 449-88.
Pedley, H. M., 1974. Miocene seafloor subsidence and later subaerial solution subsidence structures in the Maltese Islands. Proc. Geol. Ass., Vol. 85, 4, p. 533-547.
Pedley, H. M., House, M. R. and Waugh, B., 1976. The geology of Malta and Gozo. Proc. Geol. Assoc., Vol. 87, pp.325-341.
Pedley, H. M., 1978. A new lithostratigraphical and mineral resources palaeoenvironmental interpretation for the coralline limestone formations (Miocene) of the Maltese Islands. Her Majesty's Stationery Office, London.
Spratt, T. A. B., 1843. On the geology of the Maltese Islands. Proc. Geol. Soc., 4, 225-32.
Spratt, T. A. B., 1852. Geology of Malta and Gozo. Valletta. Malta.