FOSSILS AND THEIR STORY 



1089 



CALYMESE—A TRILOBITE FROM THE 

 SILURIAN. 



UPPER 



origin. All the indications point to a 

 period of stress and widespread volcanic 

 action. Of fossil remains of animal life 

 traces are few and exceedingly doubtful. 



The Palaeozoic era is one of very great 

 interest, for it is in the Lower Cambrian 

 strata that the earliest well-preserved 

 fossils have been found ; and in the rocks 

 of this era have been discovered the fossil 

 remains of many extinct species. The 

 most important fossils confined to the 

 Palaeozoic rocks are known as Trilobites, 

 and are the fossil remains of the ancestors 

 of the crabs and lobsters. The name 

 Trilobite refers to the peculiar structure 

 of each successive segment of the animal's 

 body, each segment being divided into 

 three portions or lobes. These creatures 

 had on the chest and tail segments of their 

 bodies, feet adapted for swimming, and 

 gills for breathing ; and, from the number 

 of their fossil remains, must have been 

 very numerous. In general appearance, 

 apart from their tri-lobed segments, they 

 are rather like very large specimens of the 

 so-called wood lice — which are really 

 Crustaceans — that live under the bark of 

 old, decayed tree-stumps. 



Resting conformably on those of the 

 Cambrian system are the rocks belonging 

 to the Ordovician or Lower Silurian 

 system. From the fossil remains and 

 general character of these deposits it 

 would a})pear that the geography of 

 Britain, while these rocks were being 

 formed, presented the appearance of a 

 deep-sea archipelago, somewhat like the 



138 



INTERIOR AND EXTERIOR OF SHELL OF 

 STRUI'HOMESA, FROM THE SILURIAN 

 FORMATION. 



]Malay Archipelago or the Kurile Islands, 

 the islands being chiefly volcanic. Some 

 gigantic Crustacea called Merostomata are 

 found in these deposits, and may be 

 considered an ancestral type of the King- 

 Crabs. Trilobites were also numerous, 

 and the pretty double shells of Stro- 

 phomena, a Brachiopod shell-fish, which 

 existed during some four geological periods 

 — from the Ordovician to the Carbonifer- 

 ous period. 



It is in the Silurian deposits that the 

 first fossil remains of the fishes and land 

 plants appear. The pretty little trilobite 

 called Calymene was not uncommon, and 

 Sea Lilies {Crinoids) abounded. Corals 

 were very numerous, and must have 

 formed considerable reefs in just the same 

 manner as they are doing in the tropics 

 to-day. Amongst the Corals character- 

 istic of this period, are the Hone\'Comb 

 [Favosites), the Chain Coral {Halysitcs), 

 and Omphyma. Amongst the fossil 

 Hydrozoa, the beautiful little Mono- 

 graphtus belongs to the Silurian forma- 

 tion. The ancestors of the Cuttle-fish 

 and Nautilus of to-day were well repre- 

 sented in the Silurian seas, their shells 

 coming down to us most beautifully 

 preserved. 



To the enthusiastic fossil-hunter the 

 Silurian deposits of Shropshire, North 

 Wales, the southern part of the Lake 

 District, and the southern Highlands of 

 Scotland offer a rich harvest of most 

 interesting specimens. 



In Scotland, South Wales, and Here- 



