IHE GEOLOGICAL TIME- SCALE. 



( 1 ) Chalk formation. 



(2) Ferruginous sands. 



(3) Oolitic system or series. 



/ s \ Red marie or New Red sandstone. 



(4) 



Newer Magnesian or conglomerate limestone. 

 III. Medial, or Carbojiiferoiis order. 



( 1 ) Coal measures. 



(2) Millstone, grit and shales. 



(3) Mountain limestone. 



(4) Old Red sandstone. 



De la Beche (Geology, 3d edition, 1833) carries out the 

 system more completely, calling the first, or superior order, 

 Siipercretaceous group, and applying the terms Cretaceous, Oolitic 

 and Red sandstone to three groups into which he divides the second 

 order, and giving the third the name Carboidferous group. Below 

 these he recognizes Werner's Grauwacke group, for what was the 

 lower part of the original Uebergangsgebirge of his earlier class- 

 ification, and below this were the i?iferior stratified or uon-fossilif- 

 erous rocks, and the rmstratified rocks. All of the names, it will be 

 observed, are names indicative of mineral characters. If we turn 

 back to the year 18 17 we find the same Wernerian system applied 

 to the classification of North American rocks by William Maclure 

 (Observations on the Geology of the United States of America, 

 Philadelphia, 181 7). The author writes: "Necessity dictates 

 the adoption of some system so far as respects the classification 

 and arrangement of names. The Wernerian seems to be the 

 most suitable, first, because it is the most perfect and extensive 

 in its general outlines ; and secondly, the nature and relative 

 situation of the minerals in the United States, whilst they are 

 certainly the most extensive of any field yet examined, may 

 perhaps be found the most correct elucidation of the general 

 accuracy of that theory, so far as respects the relative position 

 of the different series of rocks." (Observations, etc., p. 28). 

 The classification there set forth is as follows (in the order 

 from below upwards) : 



Class I. Primitive rocks. 



