OF UPPER CANADA AND THE WESTERN PART OF OHIO. 279 



5. At the Canada Company's Mills, about two miles above the bridge, a 

 higher set of strata appear. These consist of dove-coloured and fawn-coloured 

 limestone, abounding in characteristic fossils, overlaid by a bluish limestone, 

 weathering with a mealy surface, often coarser than the preceding, and some- 

 times slightly sparry. This also is very full of fossils. 



Though the determination of the precise date of these limestones overlying 

 the pitted rock, would supply the best link for establishing the connexion of 

 the western and eastern strata, an approximation to it is all that we have yet 

 been able to effect. That they constitute a new formation, not found in New 

 York, we think is evident; but these horizontal limestones are so extensively 

 overspread with drift, and, when, seen, expose so small a depth, as to make it 

 impossible to find their actual contact with the Onondaga or Seneca strata; 

 though they occur on the north branch of the Thames under circumstances 

 that intimate their close connexion with those rocks. We cannot, therefore, 

 assign to them their exact position; nor is it practicable to designate the neigh- 

 bourhood where the Maitland limestone first appears or the Onondaga rock 

 finally vanishes in going westward. The former originates probably east of the 

 north branch of the Thames, while the last has an assignable thickness for 

 some distance farther west. But if the exact horizon of the Maitland lime- 

 stone cannot now be defined, there is reason, on two accounts, to place it high 

 in the calcareous group which underlies the Marcellus shales. One motive 

 for assigning it this position, is its obvious identity with the Sandusky lime- 

 stone, the infra-position of which to the Marcellus shales can readily be 

 shown. 



That this identity exists we are persuaded from a comparison of fossils, and 

 from actually tracing the pitted rock and Maitland limestone, from Canada 

 round the head of Lake Erie. Another inducement for thus referrinsr the 

 Maitland stratum, is the affinity which prevails between its fossils and those 

 of the Onondaga and Seneca rocks. Of the species examined, it contains in 

 common with those formations, Atrypa afflnis, also an Atrypa common at 

 Schoharie, Strophomena lineata, a delthyris common to the Onondaga lime- 

 stone and to the shales next above the equivalent of that rock in Pennsyl- 

 vania, (Marcellus shales,) also Cyathophylum Ceratites and a Trilobite of the 

 Onondaga limestone. Though these links indicate a near approximation in 

 date, they are not regarded as proving the rock an equivalent of any of the 

 VIII. — 3 v 



