268 



NATURE 



[January 19, 1893 



of the problems presented by the former, they have re- 

 ceived the larger share of attention and have ever 

 attracted some of the most acute and philosophic of 

 scientific workers. But while the researches of such 

 investigators as Williamson and Renault into the actual 

 structures and affinities of the carboniferous plants have 

 been rewarded with the most brilliant successes, attempts 

 to speculate and theorize have only been productive of 

 barren controversy. All inferences as to the temperatures 

 in which they flourished have merely been inductions 

 from unknown data : their affinities with existing plants 

 are so remote that they can tell us of little beyond moist 

 climates and spongy, marshy soils, liable to inundation, 

 with possibly an atmosphere more highly charged with 

 carbonic acid than at present. But that neither the flora 

 nor identical conditions were uniformly present over the 

 whole land during the deposition of the carboniferous, 

 becomes every year more apparent ; and perhaps {g.\^ 

 would now maintain that fossil floras met with in widely- 

 different latitudes must necessarily be contemporary be- 

 cause similar, or reject as impossible the correlation of 

 the Glossopteris floras of the southern hemisphere 

 simply because they are so dissimilar. 



Tertiary floras, however, have to be approached from 

 almost totally different standpoints, for here minute in- 

 vestigations into vegetable structure can only excep- 

 tionally lead to important results. On the other hand 

 it may be possible to predicate the climate that any group 

 among them would have required, with almost perfect 

 accuracy. Allowing that even most closely-allied 

 species may have had different habits, enough remain 

 that are practically identical with living species. These 

 not only prove to us that in every land in our hemisphere 

 the temperatures remained warmer throughout the 

 Tertiary period than at present, but also that the tem- 

 peratures were far from equable during Eocene time. 

 Thus it is impossible to hesitate as to the evidence of the 

 flora in the lower stages of our Eocene, which exhibits 

 an abundance of planes, poplars, and alders and an ab- 

 sence of all approach to sub-tropical essences ; nor as to 

 that of the London Clay, with its tropical nipas, sabals, 

 and a host of others almost indistinguishable from species 

 existing at the present day. There is scarcely need of 

 the corroborative evidence of the Mollusca as to cooler 

 seas in the Thanets, nor of tropical conditions in the 

 large turtles, crocodiles, snakes, and nautili of Sheppey. 

 In fact, the temperature of the spots oecupied by Read- 

 ing, Bournemouth, or Mull at a particular stage of the 

 Eocene could be predicated from the fossil floras almost as 

 accurately as from living plants. Jf the same cannot be 

 said of the Arctic regions it is simply that the specimens 

 brought home are, perhaps from the exigences of travel 

 and inexperience of the collectors, for the most part so 

 imperfectly preserved and fragmentary, that few of the 

 determinations can carry the smallest weight. It may 

 suit quidnuncs to accept indeterminable fragments as 

 evidence of the growth of palms and cycads in the Green- 

 land Eocene — it is time the Miocene age of these beds 

 was relegated to the limbo of Coal-measure palms and 

 yuccas — and to become excited over the presence of a 

 sub-tropical flora within the Arctic circle ; but as a fact 

 it is doubtful whether anything has been discovered there 

 which might not have grown in our own temperature, if 

 NO. 12 12, VOL. 47] 



slightly modified, a state of things which it is conceivable 

 the damming back of the Arctic seas by the land connec- 

 tion which then existed between Europe and America, 

 aided by an active Gulf Stream, might have brought 

 about. When we come to the Miocene, worked out as 

 that of Switzerland was by Heer, or still more the 

 Quaternary, with such data as those laboriously amassed 

 by Clement Reid, the inferences as to climate are still 

 more irresistible. 



As to evidence of the age of rocks-, plants are less trust- 

 worthy, because they have neither been so perfectly 

 studied nor are their zones as yet at all properly defined. 

 All we can say is that certain assemblages are found 

 in association at the beginning of the Tertiary, and 

 that changing temperatures have since compelled them 

 not to disperse, but to migrate far and wide. Fewer pro- 

 bably of the species are extinct than is generally supposed, 

 and the primitive associations have held together perhaps 

 to the present day, with many gaps from extinction and 

 desertion and a large infusion of recruits through the 

 ordinary causes of evolution, stimulated by the increase in 

 browsing mammalia. Whether, on the other hand, the 

 marine deposit zones are really entitled to the weight at- 

 tached to them as evidences of age, except locally, is not so 

 clear. They are usually the littoral deposits of a limited 

 area, where some changes of level or current have appar- 

 ently suddenly driven out the fauna and introduced new 

 colonies more adapted to the changed conditions. If we 

 could follow the subsequent wanderings of these assem- 

 blages under the sea our faith in their sudden extinction 

 and consequently in their chronological value might be 

 greatly modified. At all events, many of the less con- 

 spicuous groups of mollusca, when critically examined, 

 prove to have surprisingly near relatives in distant seas 

 at much later periods, and even at the present day. 



J. Starkie Gardner. 



OUR BOOK SHELF. 

 Pioneers of Sdence. By Oliver Lodge, F.R.S. (London 



and New York : Macmillan and Co., 1893.) 

 This book consists of eighteen lectures on the history 

 and progress of astronomy, which were delivered by Dr. 

 Lodge in 1887. "The lectures having been found 

 interesting," he thought it " natural to write them out in 

 full and publish," and, although this can scarcely be con- 

 sidered a sufficient excuse, the intrinsic merits of the 

 work are abundant justification for its existence. In 

 Part I., " From Dusk to Daylight," the progress of 

 astronomy from Copernicus to Newton is traced in a 

 series of vivid pictures of Copernicus, Tycho Brahe, 

 Kepler, Galileo, Descartes, and Newton ; while Part II., 

 "A Couple of Centuries' Progress," brings the history 

 of gravitational astronomy from Newton down to the 

 present time. In these latter lectures Roemer and 

 Bradley are associated with the velocity of light and 

 aberration ; Legrange and Laplace with the solar system 

 and the nebular hypothesis ; Herschel with the motion 

 of " fixed " stars ; Bessel with the distances of stars ; 

 Adams and Leverrier with the discovery of Neptune ; 

 and Lord Kelvin and George H. Darwin with tides. Dr. 

 Lodge has been able, by judiciously combining clear 

 statements of scientific facts and laws with interesting 

 personal details, to give his lectures all the charm of a 

 romance. The book is an admirable introduction to the 

 study of astronomy, and no better gift for a beginner 

 could well be chosen ; while to those to whom many of 



