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stretch northward towards the southern end of Lake Iroquois. At 

 Paris some of the beds contain the characteristic hopper-shaped cavi- 

 ties. The well-marked vesicular or pitted limestone of the top of the 

 formation is likewise found here. 



The Vesicular Limestone is next described and traced. This is a 

 buff coloured, impure subcrystallinc limestone, distinguished by its 

 peculiar lenticular cavities. Being remarkable for the constancy of 

 its features and its extensive range, it proved of great importance in 

 ascertaining the super-position of the more variable strata that adjoin 

 it, and was thus used as a horizon from the Niagara river through 

 Upper Canada into Michigan and Ohio. It was traced northward, 

 from Paris to the vicinity of Guelph, and was shown to lie below the 

 south branch of the Thames at Beachville, but to immerge in the 

 north branch of the same river about 40 miles above London. 



On the Maitland river near Lake Huron, it is well exposed, with a 

 group of overlying limestone. Though destitute of fossils, it was 

 readily identified at all these points. 



The Rocks overlying the Vesicular Limestone in Upper Canada 

 are stated not to accord exactly with those which repose upon this 

 rock in New York. The important changes which this part of the 

 series undergoes in passing from the central counties of that state to 

 the districts west of the Genesee, being first shown by citations from 

 the annual reports of Mr. Vanuxem and Mr. Hall, evidence was af- 

 forded of still further modifications in Upper Canada. An opinion 

 was expressed that the corniferous and Onondaga limestones thin 

 out entirely before crossing the peninsula to Lake Huron, and that 

 the hydraulic and Seneca limestones must likewise vanish, or greatly 

 change their type. On the Maitland river, near Goderich, where 

 there is a well exposed section ; the vesicular limestone forming the 

 bottom of the group; none of the formations seen east of Buffalo could 

 be recognised. In a section of the strata exposed in the cliffs of the 

 Maitland, the pitted rock is described as immediately overlaid by dove 

 coloured and bluish limestone, sometimes of a sparry texture, abound- 

 ing in fossils. No attempt was made to determine with precision 

 the relations of this formation to the strata of western New York, as 

 no instance occurred where it was found in company with the Onon- 

 daga rock or its associates ; but the opinion is expressed that it occu- 

 pies a position high among the limestones which underlie the Marcellus 

 shales. One reason for so placing the Maitland rock, is its obvious 

 identity with the limestone of Sandusky, the infraposition of which to 

 the Marcellus shales can readily be shown. This identity is made to 

 rest on a comparison of fossils, and on an actual tracing of the pitted 



