September 11, 1885.] 



SCIENCE. 



219 



sandstone, conglomerate, sliale, limestone, and iron- 

 ore, to a thickness of hundreds and thousands of feet. 

 We are confronted, then, with the problem of a coal- 

 field, and bring to our interpretation of it the points 

 already made; viz., that every seam was formed by 

 vegetable growth in a swamp or bog near the sea- 

 level. Subsidence of the coal-forming area must be 

 invoked, and the swamps successively buried under 

 marine sediments. 



To see what some of the problems of a coal-field 

 are, let us take a concrete case. The coal-field of 

 eastern Ohio is by far the most orderly field that has 

 ever been described. The regularity and simplicity 

 of its structm-e make it the type for this whole class 

 of formations. What, then, do we find in this, the 

 simplest and most symmetrical, the least disturbed 

 and complicated, of all known coal-fields ? We find 

 a maximum of two thousand feet of strata covering 

 ten thousand square miles. There is a well marked 

 rhythmical order of arrangement of these strata. 

 The three kinds that represent the agency of life are 

 always found in close proximity. Coal standing for 

 the life of the land, limestone for the life of the sea, 

 iron-ore, equally dependent on life for its separation 

 and concentration, but blended with both limestone 

 and coal, these form vital nodes in the series, rela- 

 tively of small amount, but containing all the eco- 

 nomic interest and value. The nodes are separated by 

 the sandstone and shale, which are barren of life, and 

 owe their accumulation to inorganic forces. Meas- 

 ured against the products of life, these inorganic 

 sediments have a thickness of five or ten feet to one. 

 But note, the intervals between the vital nodes are 

 approximately equal. Turning now to the problems 

 presented by this typical field, how can we explain 

 the regularity of these intervals ? One suggestion of 

 an explanation is found in that unique contribution 

 to modern science, Croll's 'Climate and time;' viz., 

 that the carboniferous age was a period of high eccen- 

 tricity, and that the coal-seams were formed during 

 interglacial stages, — an astronomical cause for the 

 recurrence of these cycles of life, that exhibit an 

 almost astronomical rhythm and order, this is a light 

 in a dark place, albeit the light is thus far but a 

 feeble one. 



But more important questions yet remain, involv- 

 ing the extent and reach of the several seams, and 

 the laws of growth of the field as a whole. Were the 

 lowest coal-seams formed over the entire area ? and 

 may we expect their presence in the central portions 

 of the basin, if we descend deep enough ? These 

 questions, and others of like import, must be classed 

 as open, although certain general propositions which 

 it would be a pleasure to expand compel me to be- 

 lieve that they should not be answered in the affirma- 

 tive. 



On the chemical side, there are various unsettled 

 questions pertaining to coal, some of which possess 

 both theoretical and practical interest. But, although 

 they are probably not insoluble, science must sink 

 its roots deeper before it can give us full answers. 

 The microscopic structure of coal is another field in 

 which much remains to be done. It is what has been 



already done in this direction that gives us our 

 grounds of confidence in i-egard to the vegetable ori- 

 gin of coal. But the relative importance and distin- 

 guishing characters of coals formed of carbonized 

 vegetable tissue, of spores, and of hydrocarbons, are 

 still undetermined. 



In conclusion, we may be sure that the problems 

 relating to coal which now rise before us as unfin- 

 ished, will, sooner or later, find their solution. But 

 when they are solved, will all be known ? Nay, 

 verily. Out of these old carboniferous swamps, new 

 questions, larger, deeper, than any we now see, will 

 perpetually arise to stimulate by their discovery, and 

 to reward by their solution, that lox}e ofknowled'jefor 

 its own sake which makes us men. 



PROCEEDINGS OF THE SECTION OF 

 GEOLOGY AND GEOGRAPHY. 



The section opened with the eclat of a 

 masterly address bj^ its chairman, and was 

 continued with lively interest, and a fair at- 

 tendance, whicli abated only on the last da}' of 

 the session. Twenty-seven papers were read, 

 and nearly all of those elicited appreciative 

 and profitable discussion. Debate was never 

 unduly warm, and, though full, rarely wandered 

 from the text. The proper functions of the 

 association were evenly exercised ; all ideas 

 were freely criticised ; the isolated and retiring 

 student was encouraged ; the chronic talker was 

 merciful ; and the philosopher, who had evolved 

 from his consciousness a perfect theory of the 

 universe, was persuaded to defer its promulga- 

 tion. In the distribution of the communica- 

 tions by topics, stratigraphy received the lion's 

 share, rejoicing not only in the leading number 

 of contributions, but in the most important 

 paper of the session. The age of ice claimed 

 less attention than usual, and the mj'steries 

 of the archaean were unassayed. The follow- 

 ing summary of the proceedings, abandoning 

 the order of sequence of the meeting, gives 

 first place to the earth's crust as a whole, fol- 

 lows with its successive la3'ers from lowest to 

 highest, and closes with volcanism and miner- 

 alogy. Geography made no contribution to 

 the programme of the section ; but it furnished 

 the only paper accepted by the association for 

 presentation to the general meeting, — a lec- 

 ture by Capt. E. L. Corthell, on the inter- 

 oceanic problem, the substance of which has 

 already appeared in Science. 



When, in his celebrated essay, George Darwin de- 

 duced from the tidal retardation of the earth's rota- 

 tion the theorem, that the ellipticity of the terrestrial 

 figure has been diminished throughout geologic time, 

 he omitted to make certain deductions in regard to 



