CLASSIFICATION OV WATER-FORMED ROCKS. 75 



the unconformable beds might always be traced 



to a district where they become conformable, so 

 - no break in th< [jical record. 



in life between conformable 



more than the differences which 



zones of I with depth. As a pebble 



bed :ie, its life alters from 



:ie between tide marks, 



the fauna of the deeper lammarian zone. AlS 



the sand 1- - ded by a clay the fauna alters 



to the life Of the I Oralline /.oik*. Therefore there 



is, from the point of view of the existing distribu- 



its and animals, a necessary change ^( 

 life, with change in stratification, which has no 



important connection with imperfections m the 

 :d. 

 - In life and in Stratification were 

 ted by the late Sir Andrew Ramsay in the 



followi: j een the Lingula Bags and 



the rremadoc slates there is a nearly 



Complete .era and sp< md un- 



Formity is probable. There is the same 



dition between the Tremadoc slates and the 

 Arenig md between the Bala and Caradoc 



bed- id the lower Llandovery above. 



Thei Lk in species in all these 



md probably unconformity as well, 

 but the unconformity is not seen. Between the 

 Lower Llai and Upper Llandovery beds 



a break in life occurs, and marked unconformity; 

 and between the Upper Llandovery beds and 

 Wenlocl - similar evidence of a break in 



succession. The old Red-sandstone however 

 shows no sign of unconformity at the junction 

 where it succeeds the Ludlow rocks at the top of 

 the Silurian, and no break in life though both 



