198 



SCIENCE. 



[Vol.. II., No. 2S. 



ins t'>e whole subject, I was inclined to ?ay, that after 

 what had been done by Lyell, Goeppert, I.ogan, 

 Hunt, Newberry, and myself, this was scarcely neces- 

 sary; but, in view of what I have just stated, it may 

 be that all he can do will be required to rescue from 

 total ruin the results of oiir labors. 



An illustration of a diil'erent character is afforded 

 by tlie conti'oversy now raging with i-espect to tlie 

 so-called fucoids of the aTicient roclvs. At one time 

 the group of fucoids, or algae, constituted a general 

 place of refuge for all sorts of unintelligible forms 

 and markings; graptolites, worm-trails, crustacean 

 tracks, shrinkage-cracks, and, above all, rill-mark- 

 ings, forming a heterogeneous group of fucoidal re- 

 mains distinguislied by generic and specitic names. 

 To these were also added .some true land-plauts bacTly 

 preserved, or exliibiting structures not well understood 

 by botanists. Such a group was sure to be eventually 

 dismembered. The writer has himself done some- 

 thing toward this,' but Professor Natliorst has done 

 still more;^ and now some intelligible explanation 

 can be given of many of these forms. Quite recently, 

 however, the Count de Saport.-i, in an elaborate illus- 

 trated memoir,^ has come to the defence of the 

 fucoids, more especially against the destructive ex- 

 periments of Nathorst, and would carry back into 

 the vegetable kingdom many things whicli would 

 seem to be mere trails of animals. While writing 

 tills address, 1 liave received from Professor Crie of 

 Kennes a paper in which he not only supports the 

 algal nature of Rusichnites, Arthridhnites, and many 

 other supposed fucoids, but claims for the vegetable 

 kingdom even Keceptaculites and Archaeocyathus. 

 It is not to be denied that some of the facts which 

 he cites, respecting the structure of the Siphoniae 

 and of certain modern incrusting algae, are very 

 suggestive, though I cannot agree with his conclu- 

 sions. My own experience has convinced me, that, 

 while non-botanical geologists are prone to mistake 

 all kinds of markings for plants, even good botanists, 

 wlien not familiar with the chemical and mechanical 

 conditions of fossilization, and with the present 

 phenomena of tidal shores, are quite as easily misled, 

 though they are very prone, on the other hand, to 

 regard laud-plants of some complexity, when badly 

 preserved, as mere algae. In these circumstances it 

 is very difficult to secure any consensus, and tlie 

 truth is only to be found by careful observation of 

 competent men. One trouble is, that these usually 

 obscure markings have been despised by tlie greater 

 numljer of paleontologists, and probably would not 

 now be so much in controversy were it not for the 

 use made of thetu in illustrating supposed phylogenies 

 of plants. 



It would be wrong to close this address witliout 

 some reference to that which is the veritable pons 

 asinorum of tlie science, the great and much debated 

 glacial period. I trust that you will not suppose, that, 

 in the end of an hour's address, I am about to discuss 



1 Footprints nnd impressions on carboniferous rocks, Amer. 

 ourn. .?c., 1873. 



2 Koyal Swedish academy, Stockliolm, ISSl. 



3 Apropos des algues fosailes, Paris, 1SS3. 



this vexed question. Time would fail me even to 

 name the hosts of recent authors who have contended 

 in this arena. I can hope only to point out a few 

 landmarks whicli may aid the geological adventurer 

 in traversing tlie slippery and treacherous surface of 

 tlie hypothetical ice-sheet of pleistocene times, and 

 ill avoiding tlie yawning crevasses by which it is 

 traversed. 



No conclusions of geology seem more certain than 

 tliat great changes of climate have occurred in the 

 course of geological time; and the evidence of tliis 

 in that comparatively modern period whicli imme- 

 diately preceded the human age is so striking that it 

 has come to be Icnown as pre-eminently tlie ice age, 

 wliile, in the preceding tertiary periods, temperate 

 conditions seem to have prevailed even to the pole. 

 Of the many theories as to these changes which have 

 been proposed, two seem at present to divide the suf- 

 frages of geologists, either alone, or combined with 

 each other. These are, (1) tlie theory of the preces- 

 sion of the equinoxes in connection with the varying 

 eccentricity of the earth's orbit, advocated more 

 especially by Croll; and (2) the different distribution 

 of land and water as affecting the reception and 

 radiation of heat and the ocean-currents, — a tlieory 

 ably propounded by Lyell, and subsequently exten- 

 sively adopted, either alone or with the previous one. 

 One of these views may be called the astronomical; 

 the other, the geographical. I confess that I am in- 

 clined to accept the second or Lyellian theory for 

 such reasons as the following: 1. Great elevations 

 and depressions of land have occurred in and since 

 the pleistocene, while the alleged astronomical, 

 changes are not certain, more especially in regard to 

 their probable effect on the earth; 2. When the rival 

 theories are tested by the present phenomena of the 

 southern polar region and the North Atlantic, there 

 seem to be geographical causes adequate to account 

 for all except extreme and unproved glacial con- 

 ditions; 3, The astronomical cause would suppose 

 regularly recurring glacial periods of wliicli there'is 

 no evidence, and it would give to the latest glacial 

 age an antiquity wliich seems at variance with all 

 other facts; 4. In those more northern regions where 

 glacial phenomena are most pronounced, the theory 

 of floating sheets of ice, with local glaciers descend- 

 ing to the sea, seems to meet all the conditions of 

 the case; and these would be obtained, in the North 

 Atlantic at least, by very moderate changes of level, 

 causing, for example, the equatorial current to flow 

 into the Pacific, instead of running northward as a 

 gulf stream; 5. The geographical theory allows the 

 supposition not merely of vicissitudes of climate 

 quickly following each other in unison with the 

 movements of the surface, b^it allows also of that 

 near local approximation of regions wholly covered 

 with ice and snow, and others comparatively tem- 

 perate, which we see at present in the north. 



If, however, we are to adopt the geographical theo- 

 ry, we must avoid extreme views; and this leads to 

 the inquiry as to the evidence to be found for any 

 such universal and extreme glaciation as is demanded 

 by some geologists. 



