218 



SCIENCE 



[Vol. VI., No. 136. 



or three of the fields of American geology in which 

 special activity now prevails. 



I have already called your attention to the begin- 

 nings of vertebrate life on this continent, but it is 

 not in this fact that the chief interest of our verte- 

 brate geology is found. It is in the later stages 

 and higher forms of vertebrate life that American 

 geology holds an easy and undisputed pre-eminence. 

 Along the eastern slopes of the Rocky Mountains, 

 there are being disentombed the remnants of great 

 faunas of cretaceous and tertiary time that are quite 

 without parallel in the history of geology. While 

 these faunas are remarkable for the great number 

 and variety of the species and individuals, and also 

 for the enormous size of some of their forms, it is in 

 other directions that their highest interest lies. By 

 their anomalous and altogether unexpected char- 

 acters, by their strange combination and dissociation 

 of peculiarities of structure, they throw a flood of 

 light on the question of evolution, and give us a key 

 to the development of the existing creation that, 

 before their discovery, it was too much to expect that 

 we should ever possess. Here are birds with teeth, 

 here are reptiles without them. Here are animals 

 in which the characters of both birds and reptiles are 

 so blended that it is hard to tell on which side of the 

 line they belong, or whether there is any line. Here 

 are horses with four toes, and hogs that chew the 

 cud. 



The activity in the investigation of the so-called 

 archaean rocks is ' known and read of all men;' but 

 as to the progress to be reported I dare not affirm, 

 for the smoke of battle still covers the field, and the 

 clash of arms still fills the air. In no previous year 

 has there been so large and varied an amount of pub- 

 lication upon all of the problems involved as in this; 

 and the topics discussed cover the whole range, from 

 the igneous fusion of the earth, to the formation of 

 a recent volcanic cone. The discussions are charac- 

 terized by great ability, but the conclusions reached 

 are wide apart and irreconcilable. Eozoon still main- 

 tains the struggle for existence, but with apparently 

 lessening chances of survival. 



Glacial geology is still a field of decided activity 

 and progress. The most recent of geological forma- 

 tions, the drift, is still the most anomalous and 

 perplexing. We have less experience and direct ob- 

 servation that can be brought to bear on its mode of 

 formation, than we have on oceanic deposits, or even 

 on the outflows of igneous vents. But, little by lit- 

 tle, we seem to be coming into substantial accord in 

 regard to the general sequence of the events that 

 constituted the glacial period. The luminous and 

 fruitful theories of Croll, like Darwinism in biology, 

 are permeating all our modern glacial literature. 



The most important service that has been ren- 

 dered in the American field is the recent mapping 

 of the great moraine from the Atlantic border to 

 Dakota. And in view of the facts which have thus 

 been brought out, scepticism in regard to the former 

 occupation of the northern portions of the continent 

 by a sheet of land-ice moving southward would seem 

 to be impossible to the candid mind. It is coming to 



appear that the glacial record of North America is, 

 like the rest of its geological history, incomparably 

 simpler and clearer than that of Europe ; and both 

 the order of events of the last ice-age, and the nature 

 and mode of operation of the forces employed, can be 

 studied to better advantage here than elsewhere in 

 the world. 



I wish now to bring before you a few of the Un- 

 finished problems relating to the geology and chem- 

 istry of coal. 



For the last fifty years, there has been no reason- 

 able ground for doubt that coal is more or less meta- 

 morphosed vegetation, and that the plants which 

 formed the coal grew where they are now found. 

 Nearly every seam of coal is underlaid by a stratum 

 of clay containing the well-known stigmaria, which 

 have been proved to be the roots, or underground 

 stems, of the lepidodendrid and sigillarid trees com- 

 Ijosing the coal; and hence it may be truly said that 

 the rootlets of the stigmaria bind the coal-seams fast 

 to the surface of the land. Most of the well-matured 

 and more elaborate theories of coal agree still farther 

 in holding that this vegetation grew on low lands, 

 and not only near the sea-level, but near the sea itself. 

 But as we advance beyond these generally accepted 

 positions, we seem to find ourselves at once among 

 the unsettled questions; for the particular conditions 

 and modes of growth of the great sheets of coal vege- 

 tation are variously conceived and represented. 



1°. Forests growing on swampy tracts, finally sub- 

 merged, and buried under sheets of sand and clay, 

 the forest trees themselves constituting the bulk of 

 the coal: this is one of the earlier and cruder theories 

 which it is somewhat surprising to find still surviving. 

 2°. An accumulation of vegetation, quite after the 

 manner of the mangrove swamps of sub-tropical lauds 

 at the present time, makes another theory. Geikie 

 adopts this as the best picture of the conditions of coal 

 formation that we can find in the existing order of 

 things. 3°. By Sir Charles Lyell, the cypress swamps 

 of the lower Mississippi were made to do like ser- 

 vice. 4°. Fifty years ago Brongniart made the sug- 

 gestion, in an almost incidental way, that we should 

 find in the peat-bogs of to-day the analogue and rep- 

 resentative of the coal-seams. This suggestion has 

 been living and growing ever since. A young Swiss 

 naturalist was perhaps the first to expand it into a 

 definite theory. He saw that the laws of the peat- 

 bog could be applied to the coal-seam; that the only 

 key to the history of the latter was to be found in the 

 beds of fuel that are growing now, but whose roots 

 go back into past millenniums. We should have had 

 a glacier theory of the drift without Agassiz, a scien- 

 tific geography without Guyot, and, in like manner, 

 the peat-bog theory of coal would have found its way 

 here without Lesquereux; but, historically, it fell to 

 these three illustrious compatriots, fellow-students, 

 and life-long friends, to lead the way, each in his 

 own field, to these several great advances. 



I have glanced at the problem of the coal-swamp, 

 and the accumulation of a single seam; but these 

 seams are combined in great systems with beds of 



