Theories of Formation o Coal, 103 



same plan as that in South Wales ; and the coal-measures 

 there also rest upon limestone, containing organic remains, 

 " among which there is, in some abundance, a bivalve shell, 

 which Mr Logan recognised as indentical with Producta Lyelli 

 of Windsor in Nova Scotia." This limestone at Windsor, 

 Mr Lyell describes as " a lower carboniferous limestone." 

 The total vertical thickness of the coal-measures is more than 

 double that of the South Wales section, being 14,570 feet. 



a. The number of distinct beds in the section, of which 

 separate measurements are given, is 1114, from six inches 

 to 138 feet thick, without change in mineral composition. 



6. These beds consist of quartzose sandstones, grits and 

 conglomerates, and of arenaceous and argillaceous shales, all 

 of various shades of red, grey, and green, without any appa- 

 rent order of succession, sometimes one sometimes another 

 lying upon the coal, and occasionally a carbonaceous shale is 

 associated and intermixed with the coal-seams. 



c. Interstratified with these beds are seventy-six seams of 

 coal, from an inch to two feet thick, the far greater propor- 

 tion very thin. The aggregate thickness of the seventy-six 

 seams is only forty-four feet, and there is about the same 

 aggi'egate thickness of carbonaceous shale. The highest 

 seam is covered by a series of beds of sandstones, conglome- 

 rates and shales, 2274 feet thick. Beneath the lowest seam 

 of coal there are 2800 feet of sandstones and shales of the 

 same nature as those above, but having numerous beds of 

 grey concretionary limestone intercalated. Thus the coal- 

 bearitiy strata have a thickness of about 9500 feet. 



d. There are no terms attached to the word " Coal," indi- 

 cating any change of quality throughout the section. Some 

 of the seams are called " Coaly clay," others " Carbona- 

 ceous shale," mixed with the coal. The seams occur at very 

 unequal distances ; from a few inches apart to more than 

 1200 feet. 



e. As in the South Wales section, the coal-seams usually 

 rest on beds containing StigmaruE, but, in a great proportion 

 of instances, these occur not in clay but in sandstone and 

 arenaceous shale. This under bed is from a foot to twenty- 

 seven feet in thickness ; in one place an understone witl^ 



