370 ILLINOIS STATE ACADEMY OF SCIENCE 



required. All these materials are bulky, so the industry 

 can be carried on profitably only where limestone, clay 

 and coal are found intimately associated. Near the river 

 the limestone underlies a thin covering of earth, which 

 can be stripped off with ease. The limestone has an aver- 

 age thickness of 24 feet and is underlain by 16 feet of 

 clay. The coal is mined by shafts adjoining the plants, 

 though it has been found necessary to import some coal 

 from other fields in the more recent years. 



The plants in LaSalle and Oglesby employ about 1800 

 men, and produce more than 10,000,000 barrels of cement 

 annually. The marvelous development of the industry 

 has built the city of Portland or Oglesby, and stimulated 

 the growth of LaSalle and Peru, for many of the men 

 employed in the two plants in Oglesby live in Peru and 

 LaSalle. This industry is much newer than the zinc 

 smelting industry, and is still expanding extensively. 



4. Sand Products — Glass Manufacturing. 



Sand for many uses is mined at many places along the 

 Illinois river, particularly in the vicinity of Ottawa. 

 Glass manufacturing has become a great industry, first at 

 Ottawa, and later at Streator. Much sand is mined 

 cheaply at Ottawa by hydraulic methods. The glass sand 

 industry has become important locally because, first, the 

 St. Peter sandstone is soft, of even texture, and may be 

 worked with ease, in many places with pick and shovel ; 

 second, the sand is of the highest quality for the manu- 

 facturing of glass, being almost pure silica and free from 

 loam; third, with one exception this is the only outcrop 

 of this sandstone in the state which is used commercially ; 

 fourth, the sandstone occurs in bluffs that are along the 

 railroad lines in the Illinois valley, and is loaded directly 

 from the pits into the cars. The glass manufacturing in- 

 dustry in Ottawa has decreased in importance in recent 

 years, due to the difficulty of getting good fuel. In Strea- 

 tor, however, which has many coal shafts working, this 

 industry is of great importance. Two plants which spe- 

 cialize in the manufacture of milk bottles and a plant 

 which manufactures plate glass and skylight glass employ 

 a total of about 1,800 men in that city. The statement 

 was made by a superintendent of a glass factory in 



