152 ONTARIO DIVISION. 



Range and extent. Commencing a little farther west than the Clinton group, and in a 

 slender band only, the Niagara group traverses the middle and western counties of New- 

 York in a closely parallel band with the inferior mass just described. It becomes an im- 

 portant rock in INIonroe county. Its northern outcropping edge passes through Penfield, 

 Brighton, Ogdcn and Sweden. In Orleans and Niagara counties, the northern edge forms 

 an outcrop in Clarendon, Albion, Medina, Royalton, Lockport, Cambria and Lewiston. 

 Throughout this distance, the rock is not sufficiently altered in its lithological characters 

 to require comment. 



Minerals usually associated with this group. The most noted and most sought for species 

 are those which occur in the geodes at Lockport. They consist of pearl spar in crystals with 

 curved faces, the dog-tooth spar in dodecahedral prisms, and a variety of sulphuret of iron 

 in long slender prisms. Galena is rarely found in this rock in New-York. Gypsum or 

 selenite, and sulphate of strontian, are common minerals in the geodes of spar, and occa- 

 sionally cubic crystals of fluor spar. Anthracite coal is also rare, but is sometimes found. 



§ 3. Thickness of the Ontario division in new-york. 

 The combined results of the observations and measurements of the strata composing this 

 division of the New-York system, are as follow : 



Medina sandstone, which constitutes the base of the division, 350 feet. 



Clinton group 80 



Niagara shale 100 



Niagara limestone 164 



Maximum thickness 694 feet. 



§ 4. Summary of the principal facts relating to the Ontario division. 



1. This division in the State of New- York, is the least extensive, and of the least impor- 



tance of the four or five divisions under which the strata are described. 



2. The Medina sandstone and Niagara limestone are the best entitled to the appellation 



of general strata. 



3. The latter marks the termination, it would seem, of a distinct era in geological history, 



whose importance, however, can not be well estimated in New-York. 



4. The only mineral deposit of importance consists of a calcareous oolitic iron ore. 



5. Agriculturally, some of the members of this division are not only interesting, but im- 



portant, in the middle and western part of the State. 



6. The country over which this division extends, is level, but is liable, from the soft na- 



ture of the materials of which the rocks are composed, to be cut and traversed by 

 gorges and ravines, that give origin to falls and cascades, of which those formed by 

 the Genesee and Niagara rivers are the most important (Sec Plates 9 and 10). 



