lO 



NATURE 



\_May I, 1879 



molecules ; and the amount of force exerted is different 

 for different elementary molecules. Hence chemical 

 affinity is a positive force. The mutual action and reac- 

 tion between the molecular systems involves the loss (or 

 gain) of energy, but this loss of energy does not furnish a 

 complete account of the action. 



Thermal measurements enable us to determine the 

 quantity of energy entering or leaving a given chemical 

 system during its passage from one state to another. 

 These measurements, therefore, give us most valuable 

 information concerning the phenomena exhibited by those 

 chemical systems. 



The results obtained by these measurements show how 

 great is our ignorance with regard to the progress of 

 chemical reactions in general ; and they suggest many 

 exceedingly interesting problems which will doubtless ere 

 long meet with satisfactory solution. The great problem 

 of chemistry is to determine the connection between the 

 structure and the properties of molecules. To take a 

 special case, it may be asked, why is the hydrogen of 

 acids replaceable by metals under definite conditions ? 

 Many facts are known which enable us to give partial 

 answers to this question ; doubtless, thermal investiga- 

 tion, taken in conjunction with other methods of research, 

 will some day furnish the complete answer. 



Thermal measurements have already shown us that 

 allotropic changes in elementary molecules are accom- 

 panied with changes in the energy of these molecules and 

 that the same generalisation holds good with regard to 

 isomeric changes among compound molecules. But the 

 whole question of allotropy is yet in its infancy. 



The thermal method promises to throw light upon those 

 phenomena which are classed together under the name of 

 valency, and perhaps to furnish an answer to the query, 

 •why does the valency of elementary atoms vary ? The 

 new method is full of hopeful anticipations. 



M. M. Pattison MuiR 



ARE THERE NO EOCENE FLORAS IN THE 

 ARCTIC REGIONS f 



IN Nature (vol. xix. p. 124) I expressed doubt whether 

 the beds containing fossil plants in or near the Arctic 

 circle, said by Heer to be miocene, are really of that age. 

 It seemed to me then very probable, but now I may say 

 certain, that at least all those said to be lower miocene 

 are truly eocene. The article was translated in Das 

 Ausland, No. 2, 1879, and replied to by Heer in No. 8 

 (February 24) of the same journal. In this reply he, as 

 1 expected, combats my views, and, although affecting to 

 believe that I had written without thought or previous 

 study, he devotes eight columns to contradicting me, yet 

 without bringing forward any fresh evidence whatever, or 

 indicating any sources of information which I had not 

 already consulted. 



Heer contends that all the known fossil floras contain- 

 ing dicotyledons, from all lands within at least 2,000 geo- 

 graphical miles of the Pole, are either cretaceous or 

 miocene. I think, on the contrary, many of them are 

 eocene. 



The leading facts for and against the hypothesis of a 

 miocene age for so large a proportion of them may be 

 briefly summarised. 



I. The great similarity of the floras (miocene of Heer) 

 of latitude 70° to those of 47° and 46°, 98 species out of 

 363, or more than 25 per cent, being common to both, 

 even in the present state of our knowledge. This, 

 according to existing plant-distribution, precludes their 

 being of the same age, unless the more southern ones 

 grew in Alpine or even hilly regions ; but no one has 

 ever contended that they did do so. No floras so 

 much alike, and assimilating so closely to those of the 

 present day, could have grown simultaneously at the 

 same level in such widely different latitudes. 



Against this Heer states that a number of trees extend 

 from the borders of Italy to the 70th parallel, as the firs, 

 birches, aspens, bird-cherry, and mountain-ash. This 

 fact has little bearing on the subject, since the trees are 

 Alpine, or, at least, not in any way characteristic of the 

 lowland flora of North Italy or of that latitude in Europe. 

 Secondly, he says that of the fifty-nine phanerogams 

 found by Feilden in Grinnell Land between 81° 44' and 

 83°, forty-fire are European, and six of these are not only 

 found in Swiss valleys, but also in Italy. This should 

 not have been advanced, being quite beside the ques- 

 tion, unless he wishes to make believe that the present 

 floras of Grinnell Land and Italy resemble each other. 

 They are, in fact, all Alpine herbaceous plants, and have 

 nothing to do with the fossil forest floras in question ; 

 besides which, the level of the Swiss valleys in which 

 these six grow is not stated, and there is nothing curious 

 in Alpines ranging into Italy. Thirdly, of 559 species of 

 phanerogams of the Isle of Saghalien, 188 are found in 

 Switzerland. Such occasional examples of wide lateral 

 distribution among plants are well known, and might 

 often be adduced, without affecting the question in the 

 remotest degree. The present distribution of the same 

 types ol "plants, trees, &c., as those which are found fossil, 

 have alone any bearing on the subject. Heer, to sustain 

 his theory, must prove that forest floras extend in some 

 other parts of the world with a much less degree of change 

 than we have experience of in ou rcontinent, over not less 

 than 30° of latitude, and in about the same longitude. 



2. The extreme improbability that the plant remains of 

 the eocene, a far more important formation than the 

 miocene, should have been alone overlooked in a series 

 of deposits abounding in plants of immense extent and 

 thickness, and continuous, it is supposed, from the middle 

 cretaceous to the upper miocene. The absence of any 

 intelligent explanation of the complete break in the 

 sequence, which Heer's nomenclature implies, and of 

 which there is not the least stratigraphical evidence. The 

 vastness and immense extent of the formations which 

 are ascribed to miocene. The universally admitted fact 

 that continuous land existed in the north between Europe 

 and America from early eocene times, as proved by the 

 palaeontological records of both continents, and supported 

 by other considerations, and which must have left records 

 at least in proportion to those of the miocene, since vol- 

 canic, the preserving agency, was active throughout the 

 whole time. 



Heer characteristically meets these important objec- 

 tions by stating that at Eisfiord, in Spitzbergen, there are 

 1,000 feet of strata between the cretaceous and miocene, 

 which he thinks doubtless represent the eocene. It is 

 strange to find any one with the least knowledge of strati- 

 graphical geology simple enough to advance such evidence 

 as the presence of 1,000 feet of beds at a single spot, in 

 dealing with so colossal an interval as that between the 

 cretaceous and miocene, especially when the latter alone, 

 over the area, is several thousands of feet in thickness. 

 Besides Nordenskjold,' from whom Heer derives his in- 

 formation, says that the miocene (of Heer) habitually rests 

 upon the cretaceous. 



Heer further says that there is a deposit with lower 

 miocene mollusca under a miocene deposit. This is 

 exactly what I should expect ; for the same reasons that 

 make it improbable that the flora is miocene apply equally 

 to these mollusca. 



3. The much higher temperatures which prevailed in the 

 eocene than in the miocene, and which could only have 

 permitted the growth of such temperate floras in such 

 high latitudes in the eocene period, according to existing 

 laws of plant distribution. 



Although I showed seriatim that a mean temperature 

 higher by 20° F. in the northern hemisphere would in- 

 evitably have produced approximately just the series of 



' Excursion to Greenland, Geot, Mag , ro! ix. 



