PKEFACE. 



IN the following pages, the three great divisions of 

 Strata, and the three great portions of Geological 

 Time, are termed Palseozoic, Mesozoic, and Cseno- 

 zoic ; these designations having fairly won their way, 

 and being really preferable, while treating of the 

 Succession of Life, to such titles as Primary, Se- 

 condary, and Tertiary, which express something more 

 than the knowledge we actually possess, and some- 

 thing different from the idea we wish to convey. 



While speaking of the Lower Palseozoic Strata 

 and the beautiful system of Life which they contain 

 a system of the highest importance in the inquiry 

 now on hand I find it convenient to employ the 

 combination of Siluro-Cambrian, or Cambro-Silurian, 

 as the occasion suggests ; and have pleasure in thus 

 commemorating in my phrase the gigantic labours, 

 sometimes independent, sometimes associated, but 

 always successful, by which, first of all men, Mur- 

 chison and Sedgwick laid open for us these deeply- 

 buried monuments of the earliest Life on the Earth. 



