32 LOWER AND UPPER SILURIAN FORMATIONS: 



one higher platform, the Articulata or jointed animals, as 

 Crustacea, insects, spiders, and the Mollusca, or pulpy 

 animals, of which oysters, cowries, and cuttle-fish are ex- 

 amples. To all these, the Vertebrata are as a great and beau- 

 tiful superstructure upon a rustic basement, in the four great 

 classes of ascending rank Fishes, Reptiles, Birds, Mammalia. 



To resume our view of the Lower Silurian fossils : Of 

 Articulata, we have first a few examples of its lowest class, 

 the Annelides or sea worms, a group ill adapted for pre- 

 servation ; otherwise, they might have been seen in greater 

 abundance. Some which were found in a building stone at 

 Lampeter, far down in the Lower Silurians, lie in a long 

 coil, as they might be supposed to have laid themselves down 

 to die upon the sea-bottom ; they are considered as allied to 

 the nereis of the present seas. But by far the most conspi- 

 cuous articulate of the early rocks is a member of the class 

 Crustacea. 



This is the Trilobite, a marine animal to which the wood- 

 louse makes the nearest approach in general form, but marked 

 by two groovings along the length of the body, so as to pre- 

 sent a tri-lobed form ; hence the name. The animal of our 

 present seas most resembling it, is the limulus, or king- 

 crab. It is surprising how many species and even genera of 

 the trilobite lived in the Silurian seas, and in what quantities 

 their remains are found in various parts of the earth. The 

 means of locomotion possessed by the animal are not known ; 

 but from its form we must suppose it to have lived at the 

 bottom of the sea, having its eyes directed upwards and side- 

 ways. The latter organs presenting facets such as are seen 

 upon similar animals of our era, we may be said to have a 

 proof furnished to us by this humble creature, " that the 

 water of those oceans and the supernatant atmosphere, was 

 as transparent a medium at that time as it is at the present 

 day, and that therefore no material permanent alteration can 

 have resulted in either during the thousands of years which 

 have elapsed since the creation of the animal world on this 

 earth." ( 1 ). The trilobites stand low in the Crustacea, nor 



