BUILDING MATERIALS. 373 



exceptions, nearly all the rocks of this character are either too coarse and 

 fragile or too soft and friable to be of any material service. 



Soapstones of excellent quality for fire proof linings and other materials 

 which may have occasional applications in construction, will be discussed 

 under the head of Refractory Materials. 



6. CLAYS FOR BRICKS AND CEMENTS. 

 As might be inferred from an inspection of the geologic structure, sands 

 are much more abundant than the clays in our region, especially in the gran- 

 itic core of the region. Occasionally some excellent clays, both ferruginous 

 and non-ferruginous, are to be had along the borders of this tract in situa- 

 tions not far removed from the Cretaceous and Paleozoic strata. These will 

 probably attract notice from their great variety more than from their abund- 

 ance in any one locality. The conditions for the accumulations of numer- 

 ous kinds of clays have existed over much of the tract, but it will require 

 special observations to give a full statement of them. We are doing all we 

 can to accumulate facts upon these topics, but the variety of work necessary 

 to classify them is very great. 



7. DECORATIVE STONE. 



The serpentine and other rocks which might have an application as deco- 

 rative stones are not probably present in our district in such desirable forms 

 as to make them useful upon a large scale. But when the industrial develop- 

 ment of the region has assumed important proportions, many of the more 

 durable and attractive rocks not now noticed may become sources of revenue 

 on account of special adaptations. Probably some of the brilliant red sand- 

 stones and the chocolate limestones, or even the tougher greensand strata 

 may thus be utilized, although they are not commonly strong enough to "re- 

 sist heavy pressure in ordinary construction. 



8. MATERIAL FOR LIME, ETC. 



The limestones may be used in some cases for the manufacture of lime, the 

 best quality being produced from the chalky Cretaceous strata which lie 

 nearly horizontally along the borders of the district and in the great inlying 

 promontory known as the Mason Mountains. Many of the Silurian lime- 

 stones are too siliceous for making good lime, but some of them are more 

 suitable. 



The Potsdam limestone division of the Cambrian System has strata which 

 can be utilized for this purpose. 



Hydraulic limestones are not known to exist in the Pre-Carboniferous 

 rocks of the Central Region, although some of the Silurian shaly beds, and 

 even the shaly portions of the Potsdam limestone, may be worth testing. 



