FAMILIES OF ROCKS 



geologist, Mr. (afterwards Sir) Roderick Murchison, was 

 engaged in the examination of the strata which occupy 

 the south-east of Wales and the adjoining border counties 

 of England. To these rocks Murchison gave, in 1835, 

 the name of Silurian, from the ancient British tribe of the 

 Silures, who inhabited that part of the country when the 

 Romans invaded Britain." Later in last century, in order 

 to distinguish more clearly the periods of the rocks which 

 began or ended in these areas, the name of another 

 ancient British tribe was called into requisition the 

 Ordovics ; and thus for certain strata which were neither 

 Silurian nor Cambrian Professor Lapworth proposed the 

 name Ordovician. 



Let us, however, now leave these geological contro- 

 versies, enthralling as they are to those who have taken 

 part in them, to consider briefly what was the aspect of 

 the earth during the ages when these rocks were being 

 laid down. The earliest rocks do not generally contain 

 fossils, though there is no doubt that life existed during 

 the later part of the time when they were laid down. 

 The few fossils that have been preserved are those of 

 Crustacea (the species from which shrimps, for example, 

 are derived), and there are certain tracks of two kinds of 

 burrowing worms. It is noticeable that Crustacea, the 

 oldest definite fossils yet found, belong to a family which 

 is well up in the animal kingdom, and therefore we 

 know that lower forms of life must have been long in 

 existence. Since we can only draw conclusions of the 

 climate of a period from its fossil remains, and as these 

 fossil remains are so scarce, we cannot say really any- 



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