48 



Credit Member 



From the 360- to the 370-foot levels, the limy layers appear again, and 

 several species of fossils are found, the most striking occurrence being that of 

 Isotelus cf. maximus in large and numerous fragments, each fragment encrusted 

 with the bryozoan Stigmatella sessilis crassa. 



The following species occur: — 



Hallopora onealli creditensis, var. nov. 



Stigmatella sessilis crassa, var. nov. 



Zygospira modesta, Hall. 



Byssonychia radiata {Hall). 



Clidophorus planulatus (Conrad). 



Cymatonota cf. lenior, Foerste. 



Ischyrodorita unionoides (Meek). 



Modiolopsis borealis, Foerste. 



Modiolopsis concentrica, Hall and Whitfield. 



Pterinea demissa (Conrad). 



Whiteavesia pholadiformis (Hall). 



Whitella cf. hindi (Billings). 



Whitella sp. 



Actinoceras crebriseptum (Hall). 



Crinoid columns. 



Isotelus cf. maximus, Locke. 



This fauna is very different from that of the upper part of the Humber 

 member as seen at the exposures at the mouth of the Credit with its profusion 

 of Zygospira erratica and Rafinesquina mucronata torontonensis. 



Most of the species from the Credit member, however, are represented on 

 the Humber river: they indicate almost equally strong affinities with the Mays- 

 ville of Ohio and the Pulaski of New York, with a sprinkling of local Dundas 

 forms. Many of the species found in the Credit member are also found in the 

 Salmon River sandstone, and it is probable that these two subdivisions are 

 correctable. 



From the 370- to the 380-foot levels, a small number of species is found, 

 including Stigmatella sessilis crassa, Hebertella occidentalis, and Zygospira modesta. 

 The fauna alone does not give much clue as to where these ten feet of rock 

 should be placed, but they are included in the Credit member for reasons 

 appearing below. 



DuNDAS-RlCHMOND CONTACT 



It has been found that between the 380- and the 410-foot levels, the shales 

 are devoid of life, but from the 410 foot level upward, the rocks again become 

 calcareous and yield a rather large assemblage of fossils which are beyond doubt 

 of Richmond age. This 30-foot band of barren shale forms the boundary between 

 the Dundas and the Richmond. The contact cannot be sharply drawn, but the 

 faunal break is distinct, comparatively few species being common to the upper- 

 most zone of the Dundas and the lowermost zone of the Richmond. 



In eastern Ontario and Quebec, Foerste describes a somewhat different 

 set of conditions. In that area the Richmond sea entered the Maysville sea 

 very slowly, its fauna replacing the older fauna, species by species; consequently 

 for many feet above and below the boundary the fauna is not definite, typical 

 Richmond species such as Catazyga headi being found low in undoubted Maysville 

 strata, while many Maysville species such as Cymatonota lenior, Clidophorus 

 planulatus, and Cuneamya scapha brevior, range high up into the Richmond. 



