150 ONTARrO DIVISION. 



rapidly as those of Wayne, Orleans, Monroe and Niagara counties. The sliales of the 

 latter counties undergo the process sometimes called slaking, which consists in falling to 

 a powdery state even when they are dry. The change, however, is far more rapid where 

 they arc exposed to an alternate action of atmospheric agency. It is almost impossible to 

 prevent the decomposition of a piece of shale when it is wetted after having been thoroughly 

 dried. This fact teaches us the mode by which they may be converted into renovators of 

 the soil ; for it is found that tliey contain several valuable salts, which are important in 

 promoting the growth of vegetables. We sliall recur again to this subject in another place. 



Minerals usually associated with the rocks composing this group. The most important 

 mineral is the oolitic iron ore, which forms distinct strata by itself : it is a calcareo-argil- 

 laceous ore, and is used for castings, but not for bar iron. Masses of chert, in which are 

 cavities lined with quartz crystals, arc not uncommon in the layers of limestone. Sulphate 

 of barytes, of a red color, occurs in the oolitic iron at Wolcott furnace. Crystals of car- 

 bonate of lime, sulphate of lime, pyritous copper and iron, and green carbonate, are 

 sometimes found in several of the masses belonging to this group. 



Miscellaneous remarks. The most remarkable feature, as already observed, is the sudden 

 and repeated changes in the mineral type of the layers and rocks which enter into this 

 formation ; and perhaps the presence of those singular beds of iron ore, is not the least 

 interesting of the facts connected with it. That a mass whose average thickness does not 

 exceed one foot, should be spread out so extensively and by itself, unmixed with other 

 matter, is a circumstance of great interest, and worthy of sppcial investigation. The source 

 of the iron is not well determined. In Jefferson and St. Lawrence counties, the red spe- 

 cular oxide of iron is abundant ; and the beds which are now open, exhibit the fact that 

 they have at some former period suffered from denudation and transportation in a southerly 

 direction, but tliis occurrence belongs without doubt to a period long posterior to the forma- 

 tion of the oolitic iron. Still it is rational to believe that these northern beds may have 

 furnished the materials for the iron of the Clinton group ; and it is evident that these 

 masses were brought to the surface at a period subsequent to the deposition of tlie Potsdam 

 sandstone, and the event may have happened in the era of the Clinton group. There is 

 yet nothing discovered that militates against this view of the origin of the iron in question. 



The Clinton group is not confined to the State of New-York : it is found in Ohio, Penn- 

 sylvania and Canada. Its thickness in New- York, according to Mr. Hall, does not exceed 

 eighty feet. It is between fifty and sixty feet in Warren in Herkimer county. 



§ 2. Niagara group. 



Geodiferons limcrork, and Calciferous slate, of Eaton ; Lockport limestone and Rochester slate. Upper part of the 



Protean group, of the Annual Reports. 



This name, as proposed, is selected from the place where the group is best developed, 

 and where it not only is well situated to arrest the attention of the curious, but also occu- 

 pies a point more generally visited than any other witiiin the bounds of New- York. It 

 consists of only two distinct members, and hence is comparatively a small group, or one 

 which is composed of a small number of members. 



