44 THE HARMONIES OF NATURE. . 



the whole carboniferous system, whose successive stages (lower 

 carboniferous shale, carboniferous limestone, millstone grit, coal- 

 measures, upper coal grits, lower new red sandstone) frequently 

 measure no less than from 6,000 to 8,000 feet in thickness ; or 

 even as in South Wales, Nova Scotia, and near Saarbruck, 13,000, 

 14,000, and 20,000 feet ! The wings of fancy fail to carry us 

 over the vast chasm which separates the first of these deposits 

 from the last ; and yet the whole system itself is but a link in 

 the chain of successive formations of which the earth-rind, as 

 far as we are able to sound its depth, is composed. 



Truly man is but the creature of a day, and yet it is for him 

 that the primeval forests grew, that the mighty ferns waved 

 their fronds in the desert air, and that the marshy plants spread 

 their succulent leaves and stems, unnumbered ages before he 

 was to appear upon the scene. 



The alternating strata of coal and stone of which the carbo- 

 niferous system consists, can hardly be explained in any other 

 manner than by a general slow subsidence of those coasts on 

 which the vegetation flourished, alternating with periods of rest. 



During an epoch of subsidence, the humus-layer formed by 

 the deposits of ages of forest growth was inundated, and gradu- 

 ally became covered with a system of sand or mud, upon which 

 in the following period of repose a new swampy vegetation could 

 arise and continue to flourish until a new subsidence once more 

 whelmed it beneath the waters. Thus gradually coal followed 

 upon sand, or sand upon coal, until the whole mighty series was 

 built up ! 



Although all coal-fields must have originally been formed in 

 horizontal or slightly undulating situations, yet in many cases 

 they have undergone enormous derangements from the subsequent 

 action of volcanic powers. Thus, in the Belgian carboniferous 

 formation, the strata are not only violently contorted, but often 

 elevated through an angle greater than a right angle, and are 

 thus actually inverted, so that the basin -shaped depressions in 

 which the coal occurs are twisted out of place, and the whole 

 geology of the district apparently thrown into confusion. 



Faults are in fact so common in coal-strata, that they are but 

 rarely missing. They occur in every possible dimension, so that 

 sometimes the severed parts of a field have been displaced many 

 hundred feet from their original position. 



