344 Prof. H. A. Nicholson — On the ' Guelph ' Limestones. 



1863). Here they occupy a band of country which may be roughly 

 described as extending from near the western extremity of Lake 

 Ontario to Lake Huron, and they attain their maximum thickness in 

 the townships of Dumfries, Waterloo, Puslinch, Guelph, Pilkington, 

 and Nichol. They are estimated to possess a total thickness of about 

 one hundred and sixty feet, and they consist entirely of magnesian 

 limestones, which are usually of a buff, white, or yellow colour. 

 The subjacent strata, which constitute the mass of the Niagara 

 Formation, though often consisting in part of beds of magnesian 

 limestone, have a prevailing black, blue, or grey colour, and the 

 Guelph dolomites are readily recognized by this alone. The texture 

 of the rock is often highly crystalline, but it is commonly very 

 porous or almost vesicular, owing partly to the existence of drusy 

 cavities and partly to the numerous vacant spaces left by the 

 weathering out of organic remains. The exposures of the Guelph 

 Limestones which are best known are those found at Guelph, Gait, 

 Hespeler, Elora, and Fergus, and in all these localities the rocks are 

 charged with an abundance of fossils. Good specimens, however, 

 are very difficult to procure, and the great majority of examples are 

 simply in the condition of casts. Some beds of the formation yield 

 a massive and valuable building stone ; and others are burnt for 

 lime, though in this latter respect there appears to be a prevailing 

 preference for the cherty and siliceous limestones of the Corniferous 

 series. 



In the State of Ohio all the Limestones of the Niagara formation, 

 with the exception of the celebrated " Dayton Stone," are magnesian, 

 and the Guelph Limestones are consequently not distinctly marked 

 off from the lower beds by any lithological peculiarity. The summit 

 of the Niagara series in Ohio is, however, formed by a group of dolo- 

 mites, which can be unhesitatingly identified with the Guelph forma- 

 tion of Canada, not only by the precise similarity in mineral charac- 

 ters, but also by the identity of organic remains. The Ohio geologists 

 usually term these dolomites the " Cedarville Limestones," or the 

 "Pentainerus Limestone." The latter name is derived from the 

 great abundance in these beds of Pentamerus oblongus, Sow., a 

 Brachiopod which is characteristic in Canada of the base instead 

 of the summit of the Niagara series. The former name is de- 

 rived from the great development of the series at the town of 

 Cedarville, in South-western Ohio, where it is largely quarried, and 

 where I had the opportunity of examining it last spring under the 

 guidance of my friend Prof. Edward Orton, of the Ohio Geological 

 Survey. As seen at Cedarville, and a few miles to the north at the 

 village of Clifton, the Guelph formation consists wholly of beds of 

 massive magnesian limestone, usually destitute of distinct lines of 

 stratification in its lower portion. In appearance the rock presents 

 the most striking similarity to the magnesian limestone of the same 

 age in Canada, being of a yellowish or greyish- white colour, crystal- 

 line, rough to the touch, and rendered more or less vesicular by the 

 presence of numerous cavities. Fossils are abundant, but are almost 

 wholly in the condition of casts ; whilst it is a matter of the greatest 



