236 THE DEVONIAN AND CARBONIFEROUS. Ibull 80. 



The section of which Mr. Lesley gave a fall account is situated be- 

 tween Luigan and Great Glace Bays on the east coast of Cape Breton. 

 It includes the u Productive Coal Measures" of Cape Breton with five 

 workable beds. In the North Sydney measures Mr. Brown has re- 

 corded thirty-four seams, but only four of them are workable, varying 

 from 3 to 7 feet in thickness. 



The author concluded that Mr. Brown's estimate of 10,000 feet for the 

 Productive Coal Measures is too great. He added an analysis of 

 Logan's " Joggin's section " having " a vertical thickness of 14,570 ■ 

 feet," and containing "seventy-six beds of coal, and ninety distinct 

 Stiginaria underclays," and " twenty-four bituminous limestones." 



In Dr. Dawson's reply he took exception to Mr. Lesley's views under 

 the following heads : (1) It is not safe to make comparisons between 

 the greatly developed Coal Measures of Nova Scotia and the thinner 

 beds of the west ; (2) The Coal Measures were deposited on the sides 

 of the Silurian and Devonian hills in separate areas and not over the 

 hilltops ; (3) It is useless to make comparison between even the Jog- 

 gins section and those of Wallace and Pictou. "A fortiori, detailed 

 comparison with Pennsylvania and more distant localities must fail;" 

 (4) " The whole of the Coal Measures in the Jogging section belong to 

 the Upper and Middle Coal Measures. It is quite incorrect to inden- 

 tify No. 6 of Logan's section with the Lower Coal Measures ;" (5) u The 

 flora is identical throughout the whole thickness of the Middle Coal 

 Measures ;" (6) The flora of the gypsiferous deposits and marine de- 

 posits of Nova Scotia is certainly Carboniferous, while the flora of the 

 so-called u Chemung " is as decidedly Devonian. 



In a letter 1 to the editors of the American Journal of Science, Dawson 

 combats the action of some geologists in referring certain rocks, hitherto 

 regarded as Upper Devonian, to the Carboniferous period, and gives 

 facts derived from his own study of fossil plants which, he thinks, bear 

 strongly against this view. Of all the species of Devonian land plants 

 that have come under his observation, both of America and Europe, 

 only an exceedingly small number are Carboniferous. In the Carbon- 

 iferous system, in spite of numerous differences between the plants of 

 the lower, middle, and upper divisions, "there is a grand unity of the 

 fossil flora throughout." But when the Devonian is reached, there are 

 new genera and a distinct assemblage of species. The author speaks 

 of but one exceptional case, which is that of beds at Akron and Bich- 

 field, Ohio, regarded as equivalent to the Upper Devonian of New York. 

 In a small collection from these places he saw two species which were 

 identical with Lower Carboniferous forms, while the others, though 

 having a Devonian aspect, were not identical with any New York or 

 Gaspe" species. 



While it may be, he says, that in the Paleozoic period the range in 

 time of marine forms exceeded that of terrestrial life, it would be an 



I Dawaon, J. W. : On American Devonian. Am. Jour. Sci., vol. 35, 2d ser., 1863, pp. 309-311. 



