238 CARBONIFEROUS LIMESTONE. 



This limestone is usually compact, occasionally 

 granular, and containing crystals of carbonate and 

 sulphate of Hme, as at Niagara Falls. It sometimes 

 passes into magnesian and argillaceous carbonates of 

 lime. Its colour, like that of the transition, passes 

 through all shades from white to black, being col- 

 oured and variegated by metallic oxides, thus yield- 

 ing many of the most valuable marbles. When it 

 contains alumine, as it often does, it forms an ex- 

 cellent hydraulic cement. It tiontains numerous 

 fossil organic remains ; the petrifactions consisting 

 of white carbonate of lime, thus causing a most 

 beautiful appearance when the mass is polished. 

 This limestone is very rich in minerals, such as 

 lead, iron, copper, zinc, antimony, bitumen, and crys- 

 tals of various earthy minerals. It is this rock which 

 chiefly forms that vast formation which extends over 

 the whole of the United States west of the Alle- 

 ghany Mountains, and north to Lake Champlain, 

 forming the bed of Lake Erie and the precipice of 

 Niagara, as already described. 



Mr. Featherstonhaugh states that he has traced 

 the eastern border of the carboniferous limestone, 

 conforming to the course of the other mineral for- 

 mations eastof the Mississippi, more than 1000 miles, 

 running to the west of south from the State of New- 

 York, to the 35th degree of north latitude in the State 

 of Alabama ; the course is then changed, and lies to 

 •the north of vvest, leaving Little Rock, on the Ar- 

 kansas, about 30 miles to the south, and disappearing 

 between 500 and 600 miles from the Rocky Mount- 

 ains. This deposite extends uninterruptedly a geo- 

 graphical distance of at least 1500 miles from east 

 to west, underlying portions of the States of New- 

 York, Pennsylvania, Ohio, Indiana, Illinois, Missou- 

 ri, and the Territory of Arkansas on that line. In 

 Tennessee, Kentucky, Virginia, and Maryland, it is 

 bounded by a line of which the Cumberland Mount- 

 ains form a part. In the plains through which the 



