PHYSIOGRAPHY. 79 



PHYSIOGRAPHY. 



(102) GEOLOGICAL FORMATIONS. 



The greatest thickness generally in Britain is given in feet, and 

 i few of the characteristic fossils are mentioned. 



PRIMARY OR PALEOZOIC ROCKS. 

 1. AHCKLEAN OB PRECAMBRIAN. 



Laurentian (30,000). Eozoon Canadense ? 

 Huronian (10,000 to 20,000 in Canada). 



2. CAMBRIAN containing Protospongia, Annelides, Trilobites, 

 arid Brachiopods. 



Lower 



(10,000). 



Harlech and Longmynd. Paloeopyge Ramsayi. 

 Menevian. Theca. 



Upper ( Lingula flags. LingulelJa Davisii, Crustacea. 

 (6,000;. ( Tremadoc Slates. Encrinites, A star-fish. 



3. SILURIAN, TRANSITION OR GREYWACKE containing fucoid 

 plants,. graptoliteSy corals, Placoid fish, Crustaceans. 



Arenig. 

 Llandeilo. 



Caradoc - 



Lower Llandovery. ) (By some geologists) 

 ( Upper Llandovery. t Pcntamerus. 



P o e So) 1 Wenlock - Ooral 



'' \ Ludlow. Onchus ? Palcechinus, Pterygotus. 



