15'.? 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 closelj parallel band with tin- inferior mass just described. Ii becomes an im- 

 portanl rock in Monroe county. lis northern outcropping edge passes through Penfield, 

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

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

 Throughout tliis distance, the rock is not sufficiently altered in its lilhological 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 al Lockport. They consist of pearl spar in ci \ stals with 

 curved faces, the dog-tootli 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 

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

 sionally cuhic crystals of fluor sjxir. 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 folloVi : 



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



Clinton group 80 



Niagara shale 100 



Niagara limestone 164 



Maximum thickness 694 feet 



(j 4. Summary ok 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 he 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 Slate. 



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 (See Plates 9 and 10). 



