102 



Some of the pebbles are of firm limestone and are fairly 

 smooth as though having suffered wear from wave action, 

 but fossils are frequently found in the gravels from which 

 the surface markings are scarcely removed. 



The only Palaeozoic formation exposed at Thedford 

 is the Hamilton, which is estimated to be about 300 feet 

 (91 m.) thick. The characteristic rocks are blue-grey 

 clay shale and interbedded calcareous shale and limestone. 

 Fossils are very abundant and are found in a remarkably 

 good state of preservation. 



Fossils of the Hamilton Formation. 



The different strata exposed in the Thedford region 

 are indicated in the accompanying columnar section which 

 has been compiled from the various outcrops in the dis- 

 trict. 



About 80 feet (24 m.) of Hamilton shales and lime- 

 stones are exposed in the vicinity of Thedford and along 

 the banks of the Aux Sables river. The shales which make 

 up most of the thickness weather down into fine blue 

 clay. The limestones are blue-grey in colour and are gen- 

 erally firm and resistant. The section is divided into a 

 lower series of shales and an upper series of mixed limestone 

 and shales. 



1 — The lower shales are not highly fossiliferous 

 except in a few beds. The fauna characterizing them 

 includes: — 



Arthroacantha punctobranchiata Williams 



Chonetes scitula Hall 



Schuchertella arctostiatus {Hall) 



Spirifer mucronatus arkonensis Shimer and Grabau 



Stropheodonta demissa (Conrod) 



Tentaculites attenuatus Hall 



Platyceras buccultentum Hall 



Bactrites obliqueseptatus arkonense Whiteaves 



Tornoceras uniangularis (Conrad) 



Phacops rana (Green) 



2 — At the base of the upper division is a four-inch bed 

 of limestone succeeded by six inches of black carbonaceous 

 shale. This black shale is very persistent and always 

 contains many compressed specimens of Leiorhynchus laura 

 (Billings) along with Styliolina fissurella (Hall). 



