GENERAL INFERENCES. 93 



hot-blast furnaces in operation, each smelting at the rate of 

 sixteen to twenty tons of pig-iron daily, or about 6240 annually, 

 and thus yielding a total of G24,100 tons. The market price 

 for the article, in this crude condition, is now about £3 per ton. 

 Hence the annual value of metallic ore, extracted from the 

 coal-fields of Scotland, is £1,872,300, nearly two millions ster- 

 hng ; for a product wdiich the flora of the age yielded, over and 

 above the still richer mines of the combustible elements of the 

 coal itself 



And yet there are circumstances connected with the 

 ingredients and physical arrangements of the coal-mea- 

 sures, more marvellous even than anything now stated. We 

 allude to the hmestones, and more especially to the en- 

 crinital portions of the formation. This mass of calcareous 

 matter, often sixty feet thick, as at Silver Mine Quarry, near 

 Linlithgow, consists almost entirely of shells and skeletons of 

 other marine animals. This limestone is co-extensive with the 

 coal-measures throughout the world, feathering out and in 

 among the metals, often in the form of a vertical wall, separat- 

 ing the basins of one district from those of another, and more 

 generally underlying the coal-beds in such a manner, as at the 

 same time to constitute the outer lip or edges of the great 

 trough of the carboniferous formation. Encrinites are corals. 

 They belong to the same zoophytic class of creatures which are 

 now piling up the coral reefs in the Pacific. They are composed 

 of similar varieties ; they wrought after the same fashion ; they 

 made corresponding diversities, according to the conditions of 

 their ocean bed, of the ring, atoll, and lagoon structure of coral 

 reef ; an,d they left their skeletons to construct the vast moun- 

 tain limestone strata under consideration. These strata are 

 common to all parts of the w^orld. They exist in Melville 

 Island, in Greenland, and in every coal territory washed by the 

 Northern Ocean ; and in like manner over the central and 

 southern licmispheres of the earth's surface. Like the coal 

 plants, the polyps of the ancient seas were ubiquitous, abound- 



