RELATION OF UN5TRATIFIED TO STRATIFIED ROCKS. 39 



to show the manner in which all stratified rocks have at 

 various periods been disturbed, by the intrusion of unstratified 

 crystalline rocks; and variously affected by elevations, 

 depressions, fractures, and dislocations ; fourthly, to give 

 examples of the alterations in the forms of animal and vegeta- 

 ble Hfe, that have accompanied these changes of the mine- 

 ral conditions of the earth. 



From the above section it appears that there are eight 

 distinct varieties of the crystalline unstratified rocks, and 

 twenty-eight well defined divisions of the stratified forma- 

 tions. Taking the average maximum thickness of each of 

 these divisions, at one thousand feet,* we should have a 

 total amount of more than five miles ; but as the transition 

 and primary strata very much exceed this average, the 

 aggregate of all the European stratified series may be con- 

 sidered to be at least ten miles. 



CHAPTER IV. 



Relation of Unstratified to Stratified Rocks. 



I SHALL enter into no farther details respecting the compo- 

 nent members of each group of stratified rocks, than are 

 represented by the fines of division and colours upon the 

 section.f They are arranged under the old divisions of 



* Many formations greatly exceed, whilst others fall short, of the average 

 here taken. 



t For particular information respecting the mineral character and or- 

 ganic remains of the strata composing each series, I must refer to the 

 numerous publications that have been devoted to these subjects. A most 

 convenient summary of the contents of these publications will be found 

 in De La Beche's Manual of Geology, and in Von Meyer's Paljeologica, 

 (Frankfurt, 1832;) ample details respecting the English strata are given 



