Feb. 1 8, 1875] 



NATURE 



315 



The Ramie, or China grass plant (Bahmeria tiivra), which has 

 excited so much interest of late owing to its proposed extended 

 cultivation in India, seems to thrive in Cayenne, specimens 

 having been shown at a recent exhibition in that colony and 

 compared with plants grown in France. The Cayenne plants, 

 which were grown on a comparatively poor soil, without manure 

 and with little or no attention, were double in size and height to 

 those grown in France. Three successive shoots were produced 

 in one year. 



The additions to the Zoological Society's Gardens during 

 the past week include a Peguan Tree Shrew {Tupaia pcguana) 

 from Burmah, presented by the Hon. Ashley Eden, new to the 

 collection ; a Cinereous Sea Eagle [IlaUaclus albicilla] from 

 Japan, presented by C apt. Sidney T. Bridgeford ; two Bonnet 

 Monkeys (Macacus railiatus) from India, presented by Sir F. S. 

 Gooch, Bart. ; a Sykes's Monkey { Ccrcopitheais allioguhris) 

 from Africa; a Robbin Island Snnke [Corciidla p/iocani/n) ; 

 a Horned Viper {Vipera cvn/nta), fiom S. Africa, deposited; 

 four Four-spotted Opossums {Didelphys opossum) from South 

 America, purchased. 



THE PAST AND FUTURE WORK OF 



GEOLOGY* 



II. 



" W^ '^°"' '^"''■'^ '° '^^ more special ground of the geologist. 

 Starting with investigations connected with the origin of 

 the globe, he has to trace the changes it has undergone through 

 the various phases of its history, to determine the causes of those 

 changes, and the manner in which they were effected. Besides 

 dealing with inorganic matter, he has also to study the character 

 and distribution of all organised things inhabiting the earth in all 

 former periods, their order of succession, and the relation of the 

 several and successive groups one to another." 



Referring to the theories of the other geologists and to the 

 philosophy of Hutton, Playfair, and their successors, Mr. 

 Prestwich said it is a question whether the license which formerly 

 was taken with energy is not now taken with time. Small 

 forces long continued, action frequently repeated, and maintained 

 uniformity of operation, are accepted as sufticient to account for 

 the formation of our hills and plains, for the Alps and the Andes, 

 and for all the great general as well as special features of the 

 earth's crust. 



The points at issue are, firstly, whether our experience on 

 these questions is sufficient to enable us to reason from analogy ; 

 and secondly, whether all former changes of the earth's surlace 

 are to be explained by the agency of forces alike in kind ami 

 rftgrer with those now in action. Mr. Prestwich then states his 

 reasons for answering these questions in the negative : — 



" The value of experience with respect to natural phenomena 

 depends upon whether they are symmetrical and not variable, or 

 whether they are variable and unsymmetrical. In the one case, 

 as any one part bears a given uniform relation to the whole, if 

 one part be known the whole can be inferred ; but in the other 

 case, where the whole is made up of unequal and not uniform 

 parts, the value of the evidence is merely in proportion to the 

 number of those parts independently determined, or to the ratio 

 between the duration of the observation and the duration of the 

 time comprising all the phases of the particular phemonenon. 

 Thus the path of a planet, the date of an eclipse, or the return 

 of a comet, may be predicted with certainty by the determination 

 of mere minute sections of their orbits, which in respect to time are 

 infinitely small compared to the length of the cycle of revolution. 

 On the other hand, the metamorphosis of an insect, the mean tem- 

 perature of a place, or the character of a volcano, can only be accu- 

 rately determined by a length of observation sufficient to embrace 

 all the variations they respectively present in their several cycles 

 of change. In the case of the insect, the time must be equal to the 

 duration of the metamorphosis ; in that of temperature a suc- 

 cession of years is needed to obtain a mean ; and with respect to 

 volcanoes, centuries may often pass before we become acquainted 

 with all the irregular exhibitions of their spasmodic activity. 



* Inaugural Lecture of J. Prestwich, F.R.S., Professor of Geology in 

 the Uiiiversiiy of Oxford. Delivered January 29. Continued from p. 292. 



" The necessity for a much greater extension of time becomes 

 yet more imperative when we come to deal with geological 

 phenomena, such as those due to the action of elev.atory forces 

 which are extremely varied in their nature, — being at one time 

 exhibited by a raised beach a few feet high, and at another by 

 a mountain chain whose height is measured by miles ; or by 

 the small displacement produced by an earthquake, and the 

 rectilinear fracture of a county with a displacement of thousands 

 of feet. 



"In talcing into consideration the weight of the evidence where 

 the series is so variable and irregular, it is oiear th.it the incre- 

 ment of value is only in proportion to the increment of time. One 

 phase of the insect life, one year's record of temperature, a cen- 

 tury's observation of the volcano, give evidence which, although 

 of v.ilue/?D tanto, as one link in the chain, is entirely inconclu- 

 sive when applied to the whole length. So in respect to such 

 geological changes as those just named, the value of our expe- 

 rience is only in the proportion of the length thereof to the 

 duration or cycle of the phenomenon under investigation. Thus 

 the elevation of mountain ranges have been events of rare and 

 distant occurrence. It has been estimated that all the great 

 chains can be referred to thirteen epochs : taking subordinate 

 ranges, the elevation of the main mountain chains of the old 

 world may certainly be limited to twenty such periods. Divide 

 geological time (since the sufficient consolidation of the crust of 

 the earth) by this or even by double this number, and we may 

 form some conception of the length of the cycles involving 

 changes of this magnitude. What that time was it is impossible 

 to say ; we can only feel how infinitely it exceeded all our limited 

 experience. With respect thereto the experience of five hundred 

 years is no doubt of value — one or two thousand years add further 

 to it ; — but after all, how insignificant that duration of time is com- 

 pared to the time over which the cycle extends ; it may be as 

 I : 100, or it may be as i : 200 or more, and I shall show pre- 

 sently that there are circumstances which indefinitely extend 

 even tliese proportions. I conclude, therefore, that our experi- 

 ence in these cases is by far too limited to furnish us with reliable 

 data, .and that any attempt to reason solely from part to the 

 whole must prove fallacious. Another argument adduced in 

 support of this theory is, in my opinion, equally untenable. 



" It is asserted that taking the degree of elevatory force now in 

 operation, and allowing quantity ot time, the repetition of the 

 small changes on the surface witnessed by us would produce in 

 time results of any known magnitude, i.e. that the force ^^hich 

 could elevate a district 5 feet in a century would suffice in i :o,ooo 

 years to raise it 5,000 feet. This reasoning might be con- 

 clusive if we had cause to suppose that the force were uniform 

 and constant ; but even our limited experience shows this to be 

 irregular and paroxysmal, and although the effects indicate the 

 nature of the force, they in no way give us a measure of its 

 degree. 



" Before I proceedjfurther I must remove two objections which 

 have been urged against what has been called the cataclysmic 

 theory in opposition to the uniformitarian theory, both terms in 

 themselves objectionable from their exaggeration, as all such 

 terms usually are. One is, that we require forces other than 

 those which we see in operation ; and the other, that it is unneces- 

 sarily sought to do by violent means that which can be equally well 

 elTected by time. It is not, however, a question we raise as to the 

 nature of the force, but as to its energy — it is not a question of 

 necessity one way or the other, but of interpretation ; it is a question 

 of dynamics and not of time, and we cannot accept the introiuc- 

 tion ol time in explanation of problems the real difficulties of which 

 are thereby more often passed over than solved. Time may and 

 must be used as without limits; there is no reason why any 

 attempt should be made either to extend or to curtail it ; but 

 while therejs no need for frugality, there is no wisdom in prodi- 

 gality. After all, it will be found that whichever theory is 

 adopted, the need will not be very different ; the mountain range, 

 for the gradual elevation of which the one will ask 100,000 years, 

 the other may require for its more sudden elevation a force 

 taking the same number of years to accumulate its energies. 



" We must, however, judge of the past by the features it has 

 stamped on the land, * and thfse we must interpret not entirely 

 by our own experience, not alone by our estimate of force, but 

 by our knowledge of what amount of force the energy due to the 

 thermal condition of tlie globe can develop on known dynami- 



• The eyidence of facts with respect to the glacial period has already led 

 to the admission of a greater intensity of cold : so we contend that the 

 evidence of the past is equally definite respecting the greater intensity of 

 energy 



