49 



Richmond Formation 



Erindale Member 



The first fossiliferous rocks, after the barren zone marking the boundary of 

 the Dundas and the Richmond is passed through, are also shales of the same 

 character as the shales of the Dundas formation, but containing Strophomena 

 varsensis and numerous examples of Hebertella occidentalis . 



Zone of Strophomena varsensis. — The shales referred to above mark the 

 base of the Strophomena varsensis zone, which forms the lower part of the Erindale 

 member. Above, calcareous bands become more common and Strophomena 

 varsensis much more abundant, and at the 420-foot level a bryozoan reef occurs. 

 This reef is one of the most characteristic beds in the whole Credit River section. 



An exposure of Erindale shale and sandstone on the Credit river near Streetsville. 



It consists of compact crystalline limestone, varying in thickness from four to 

 18 inches. In places it forms a single massive stratum, while at other places, 

 usually where it is thickest, it is separated into two or three strata by thin 

 layers of shale. It is full of Heterotrypa definita, a species of Bryozoa herein 

 described as new. This species is easily recognized in the field by its robust 

 branching zoaria and by the fact that the surfaces are covered with well-marked 

 maculae. It is almost confined to the reef, only a few specimens having been 

 found at any other level. Heterotrypa prolifica, Ulrich, and Stigmatella hybrida, 

 another new species, are confined to the reef but are much less abundant than 

 Heterotrypa definita. Eight feet above the reef, at the 428-foot level, the stratum 

 of limestone which marks the top of the zone of Strophomena varsensis makes its 



4 S.P. 



