TIIK SUCCESSION OF STRATIFIED K< > 



11 



gradual growth, and yet the persistence of specie* through tin- 

 Carboniferous Limestone Scries is truly rvmurkalil.-, whil.- tin- 

 limestones of the Jurassic and Cretaceous periods, though of far 

 less thickness, are divisible into numerous palicontological zones 

 or belts, each having many species which do not appear in the 

 next The changes in the forms of life inhabiting any marine 

 area being thus more rapid in later geological times, an equal 

 amount of change would naturally be accomplished in leas time, 

 and consequently, if systems are to be measured by palaxmtological 

 difference, the newer systems must include less thicknesses of rock. 



But even when allowance is made for this, it is impossible to 

 regard the divisions of Tertiary time introduced by Sir Ch. Lyell 

 as being of the same relative importance as the systems of older 

 date with which they are usually ranked. Even the Eocene, as 

 understood by Lyell, was hardly of the same palseontological value 

 as Cretaceous or Silurian, while the Miocene and Pliocene are still 

 less entitled to rank with such systems. The Oligocene has been 

 created at the expense of Lyell's Eocene, but it is now admitted 

 that these two together form a group which may rank as a system, 

 while the remaining three groups, Miocene, Pliocene, and Pleistocene, 

 may be regarded as making up another system of deposits. For 

 these two systems M. Hohnes has proposed the names Palaogen* 

 and Neogene, and though they are not altogether satisfactory the 

 names have been largely accepted on the European continent 



Systems are divided into sections or formations, which are 

 usually denominated as Upper, Middle, and Lower, unless any 

 special names have been proposed for them. These sections are 

 again divided into stages or groups, to which local names are 

 generally given, and these again are often divisible into zones. 



The following is a tabular view of the twelve fossiliferous 

 systems which overlie the Archaean rocks, together with their 

 primary divisions, according to the nomenclature which will be 

 adopted in this volume, and is applicable to the greater part of 

 Europe, This list of systems is merely a table from which no idea 

 of relative thickness can be obtained, but the adjoining columnar 

 view is drawn to scale and is intended to give some idea of the 

 relative thicknesses of these systems. 





