NIAGARA LIMESTONE. 381 



certain portions of the lower members in this respect has already been 

 considered, and the higher members now claim attention. 



The following analyses show that the first great essential, purity, ia 

 possessed in a high degree: 



~No. 1 is from the Pentamerus layer at Pelton's quarry, Pewaukee. 

 This layer is not now burned for lime, the upper layers, which are 

 purer, being used exclusively. No. II is from Mr. Horlick's, and 

 No. Ill from Mr. Beswick's quarries, Racine. All the foregoing 

 analyses are by Prof. Daniells. No. IY is an average of six analyses 

 of as many layers of Mr. J. Druecker's quarry, near Port "Washing- 

 ton, by Mr. Bode. It will be observed that the average insoluble res- 

 idue of those that are used for lime is less than one-half of one per 

 cent.; or, if the alumina and iron be included, but little over one per 

 cent. These are not analyses of exceptional specimens, but are be- 

 lieved to be fair averages of the rock used for the market product, and 

 inexhaustible quantities of equally excellent material are readily acces- 

 sible. The material used by the leading lime-burners at other points 

 is of essentially the same excellent quality. 



Aside from chemical purity, a certain degree of porosity is desira- 

 ble, since it promotes the ready escape of the gases and secures a 

 uniform and complete reduction without an excessive heat and the 

 consequent partial vitrification of the surface and loss of strength. 

 It likewise facilitates complete slacking when used, thus tending to 

 reduce the liability to slack in the wall, which is the annoying habit 

 of some limes when carelessly used. The more minutely and uni- 

 formly porous the rock is, the better. The formation under consid- 

 eration presents abundant deposits that possess this desirable quality 

 in an eminent degree, and this kind of rock is now almost exclusively 

 used, the practical experience of burners having led to this, without, 

 perhaps, fully appreciating the reason for it. 



Owing to these excellencies, the Wisconsin limes produced from 



