162 SHIMEK AND GRABAU — HAMILTON GROUP OF THEDFORD 



at Bartlett's mills about 30 feet are shown. The upper portion of this 

 series contains few fossils, in so far as we were able to judge from our brief 

 examination. Logan (page 382) mentions in his section on the Riviere 

 aux Sables a 4-foot bed of shale containing " Spirifer mucronatus and 

 other fossils." This we have not observed. . We found, however, the 

 talus below the Encrinal limestone covered with weathered-out speci- 

 mens of Sp. mucronatus var. thedfordensis fallen from the upper beds. 



The most interesting portion of the lower shales is comprised within 

 the lower 10 feet of the mass exposed at Bartlett's mills. In this portion 

 a number of calcareous layers are found, in which the most characteristic 

 fossil is Spirifer mucronatus var. arkonensis S. & G. For a description of 

 this variet}' see below. This shell often constitutes thin beds in which 

 scarcely any other fossil is to be found. It is entirely restricted to the 

 lower shales (bed 1) and apparently to the lower 10 feet at Bartlett's mills. 

 It is not found at the Brickyard, where the section is not deep enough, 

 nor has it been observed at Rock glen. 



Among the other fossils which appear to be restricted to the lower 

 portion of this lower series are Platyceras arkonense, Arthroacantha puncto- 

 brachiata, Tentaculites attenuatus var., and Bactrites obliqueseptatum var. 

 arkonense. 



The following generalized section of the exposed Hamilton beds of 

 the Thedford region is therefore derived : 



9. Calcareous Ceratopora and Bryozoa beds 10/ 



8. Shales with Spirifer beds at the base 8/ 



7. Argillaceous limestone 1.5' 



6. Blue calcareous shale . . 18/ 



5. Calcareous shales and shaly blue limestones 6/ 



4. Argillaceous limestone with Styliolina 1.5 / 



3. Coral layer 3.25' 



2. Encrinal limestone , 3/ 



1. Blue shales — lower Hamilton, the lower portion with calcareous fossil- 



iferous beds 30/ -f 



Total thickness exposed 81.25+ 



This gives us 48 feet for the upper shales and calcareous beds and 30 

 for the lower. We are not aware of any accurate determination of the 

 total thickness of the Hamilton formation in Ontario. Logan (page 

 387) cites a well record which gives a thickness of nearly 230 feet of 

 Hamilton shales penetrated below 60 feet of drift without reaching the 

 Onondaga limestone beneath, and he argues from this that the total 

 thickness must be in the neighborhood of 300 feet. If this estimate is 

 correct, we should expect to find the greater part of this mass below the 

 Encrinal limestone, since we find the outcrop of the black bituminous 



