CLAYS. 391 



The excellence of the Golden fire-clay as a refractory material is 

 largely ilue to the small percentage of the bases, potash, soda, lime, 

 magnesia, and iron, which, in the presence of quartz, readily form with it 

 fusible silicates. The percentage of tree quartz in the sample analyzed 

 was estimated from the total silica on the basis of alumina present in pure 

 kaolinite. The same method was employed in regard to the hygroscopic 

 water. Of the bases the iron has the widest range in the quantity present, 

 and requires special attention in hand-sorting the clays for the several uses 

 for which they are employed. The mixing, tempering, and general treat- 

 ment of the clays depend upon the product to he turned out; being 

 matters beyond the scope of this work, they were not investigated. 



The amount of fire-clay annually mined in the region about Golden 

 rarely falls below 4,000 tons and often considerably exceeds this. From 

 other portions of the field a possible output of 2,000 tons more is derived. 

 A large amount of the clay is manufactured into crucibles, scorifiers, muffles, 

 and furnaces, all of the very finest quality, while the remainder is consumed 

 in the fire-brick industry. 



Fire-clays also exist in the Laramie formation in connection with the 

 coal, usually forming the floor of the bed, hut they are of inferior quality 

 and of too slight and irregular thickness to be of economic importance. 

 They are frequently replaced by sandy beds. 



CLAY FOR THE MANUFACTURE OF BUILDING MATERIALS. 



The clays employed in the manufacture of general architectural mate- 

 rials are derived mainly from the upper half of the Fox Hills formation, 

 especially from a zone 300 or 400 feet thick a short distance below the 

 capping sandstones. The clays are slightly arenaceous, of marked homo- 

 geneity in constitution, and quite free from the concretionary limestones 

 which are characteristic of lower horizons in the formation. Present 

 developments are confined chiefly to the vicinity of Golden and Valmont, 

 but there are many localities along the base of the foothills favorable for 

 the establishment of brick industries. The high angle of inclination in this 

 region is well calculated to secure for the clays prior to their conversion 

 into bricks, and, therefore, for their resulting product, a uniformity of 



