PREFACH. 
As the publications of a Geological Survey cannot properly be 
limited to the maps and sections, but would be incomplete without 
figures and descriptions of the fossil organic remains made use of 
for the determination of the geological ages of the different 
geological formations of the country,* it has been determined to 
issue a “ Prodromus” or preliminary publication of the Victorian 
Organic Remains in Decades, or numbers, of ten plates each, with 
corresponding letterpress, on the plan of the Decades of the 
Geological Survey of England, followed by the Geological Surveys 
of Canada, India, and several other Governments. 
The Decades will contain figures and descriptions in the first 
place of the more characteristic fossils of each formation, of which 
good specimens may be in the National Collection ; so that 
observers in the field may make use of them for preliminary or 
approximate determination of the geological ages of the strata they 
may meet. A portion of the impression of the plates will be kept 
back until a complete systematic treatise on the fossils of each 
formation may be issued when the materials approach completion. 
This Fifth Decade contains illustrations of numerous fossils of 
the Tertiary and Upper and Lower Silurian formations, the right 
* “ Palzontological researches forming so essential a part of geological investigations, such as 
those now in progress by the Geological Survey of the United Kingdom, the accompanying 
plates and descriptions of British fossils have been prepared as part of the Geological Memoirs, 
They constitute a needful portion of the publications of the Geological Survey.”—Sir Henry 
T. De la Beche, Director-General of the Geological Survey of the United Kingdom, in notice 
prefixed to the first of the Decades of the English Geological Survey. 
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