184 



NATURE 



[June 23, 1892 



the coarser stratified rocks — grits, sandstones, &c. — lends some 

 support to this view, by showing that, as we go back in time, a 

 larger proportion of their materials, cateris paribus, has been 

 derived from crystalline rocks, and that even the fragments, 

 obviously of sedimentary origin, exhibit signs of some mineral 

 change ; that is to say, the mudstones and sandstones in the 

 later grits are apt to be represented in the earlier by phyllites 

 and quartzites. 



So the results of microscopic study, in alliance with, not 

 divorced from, work in the field, lead us to the conclusion that 

 in the early ages of this globe's history conditions generally pre- 

 vailed which became gradually, perhaps even rapidly, rare and 

 local ; or, in other words, that in geology the uniformitarian 

 doctrine must not be stated in terms wholly unlimited, though, 

 since this was first enunciated by Lyell, nothing has been dis- 

 covered to shake our faith in its general truth, or to resuscitate 

 the catastrophic hypothesis which it replaced. But geologists 

 are forbidden by students of physics to regard the universe as a 

 "self-winding clock." The latter affirm, and the former frankly 

 admit, that this globe through long ages has been losing heat by 

 radiation ; that there was a time when the temperature of its 

 surface far exceeded that of molten iron : a temperature which 

 now would be reached only at a depth of many miles. If this 

 be so, the conditions under which rocks were formed on the 

 surface of the globe in early days must have been very different 

 from those which subsequently prevailed. Suppose, for example, 

 this surface to have been just white-hot — namely, at a tempera- 

 ture much below that at which most, if not all lavas, consolidate. 

 In that case the ocean would be vapour, and the weight of the 

 atmosphere would be augmented by that of a shell of water of 

 the area of the globe, and two miles in thickness ; or, in other 

 words, the atmospheric pressure would be about 350 times its 

 present amount. If so, even a lava-flow would consolidate under 

 a pressure equivalent to that of some 4000 feet of average rock. 

 But after the surface temperature had become low enough to 

 permit the seas to be gathered together, and the atmospheric 

 pressure had become normal ; after j-ain and rivers, winds and 

 waves, had commenced their work ; after sediments, other than 

 the "dust and a-hes" of volcanoes, had begun to accumulate ; 

 still these at a short distance below the surface would find a very 

 different environment from that which now exists. It has been 

 proved by Lord Kelvin that at the end of about one twenty-fifth 

 portion of the whole time which has elapsed since the first 

 solidification of the earth's crust, the underground temperature 

 must have risen at nearly six times its present rate. To reach a 

 zone, the general temperature of which is 212° F., it would 

 now be necessary to descend, as a general rule, at least 8200 

 feet, and probably rather more. But in those early days the 

 crust would have been at this temperature at a depth of about 

 l6cx) feet, and at 10,000 feet it would have risen to 1050° F., 

 instead of 250° F., which now would be exceptionally high. To 

 this depth many rocks, both in Palseozoic and later ages, have 

 been buried, and they have emerged practically unchanged. 

 Hence it follows that the latter temperature is comparatively 

 ineffective ; the former, however, could not fail to facilitate 

 mineral changes and the development of coarsely crystalline 

 structures. 



These changes, these structures, have been produced in sedi- 

 mentary rocks in the immediate neighbourhood of a large mass 

 of intrusive igneous rock, such as a coarse granite. To what 

 temperature the former have been raised cannot be ascertained. 

 Suppose, however, it were 1500° F., which probably is not a 

 very erroneous estimate, this temperature, at the epoch men- 

 tioned, would be found at a depth of 15,000 feet. It is now, 

 probably, at least 15 miles beneath the surface. In other words, 

 the zone at which marked mineral changes could be readily pro- 

 duced, quickly sank, and has long since reached a depth 

 practically unattainable. The subterranean laboratory still 

 exists, but the way to it was virtually closed at a comparatively 

 early period in the earth's history. 



Another effect of this rapid downward increase of temperature 

 must not be forgotten. When it amounted to 1° F. for every 

 10 feet of descent, a temperature of 2000° F. would have been 

 reached at a depth of not quite four miles. This would be 

 rather above the melting-point of many rocks, if they were at the 

 surface ; so that, even under the pressure, they would be either 

 very near it or imperfectly solid. If the thickness of the crust 

 were only about four miles, flexures would be readily produced, 

 and the effects of tidal stresses would be considerable ; but even 

 if the earth had become solid as a whole, there would have been 



NO. II 82, VOL. 46] 



large masses of rock, comparatively near to the surface, in ai* 

 unstable condition, and thus liable locally to slow deformations^ 

 displacements, fluxional movements, and intrusion into other 

 masses already at a high temperature, with the result of partial 

 melting down and mutual reactions. Disturbances such as 

 these, slow, but constantly recurring, would jiroduce structures 

 imitative of stratification. It is a remarkable coincidence, to 

 say the least, that these structures are characteristic of Archaean 

 rocks, and are extremely rare, if ever present, in those of later 

 date. 



But some geologists are so rigidly uniformitarian as to shrink 

 from admitting that any portion of the earth's original crust can 

 possibly be preserved. "Take time enough," they say, "and 

 the changes can be made." But will time alone suffice for 

 every kind of change? How long will it be before gunpowder 

 explodes at blood-heat ? But passing over this obvious difficulty, 

 we may ask : Is there time enough ? So geologists once 

 thought, as fancy travelled back over endless seons. But they 

 are checked by the physicist : "earth and sun alike," he affirms^ 

 " are masses subject to the laws of radiation; these countless 

 millions of years of which you dream will bring you to a period 

 when not only the earth, but also the whole solar system, was 

 nebulous. All the history of your planet, physical as well as- 

 vital, so far as it can be covered by your lecords, must be com- 

 pressed into a very moderate number of millions of years, for 

 we have to consider the possibilities not only of a cooling earth,, 

 but also of a cooling sun." If this be so, and it seems difficult 

 to dispute the decision ; if we are forbidden to look back along 

 " the corridors of time" till they vanish in the perspective of 

 infinite distances, it becomes more and more probable that the 

 whole volume of the earth's history is within our reach, and 

 that its opening chapters will some day be deciphered. 



The progress which has been made since the microscope was 

 pressed into the service of geology augurs well for the future, if 

 we work in a spirit of scepticism and a spirit of hope. Of scepti- 

 cism, lest we trust too much either in ourselves or in even the 

 princes of science ; for experience proves that the seductive 

 charms of phantom hypothesis may lead all alike astray from^ 

 the narrow path of truth into the morasses of error. Of hope, 

 for experience also proves that by patient labour and cautious 

 induction many an illusion has been dispelled and many a dis- 

 covery been made. Our eyes must soon grow dim, our hands^ 

 become nerveless, but other workers will be found to lake 

 warning from our mistakes and to profit by our toil. The veil 

 which shrouds the face of Nature may be never wholly with- 

 drawn, but its fringe has been already raised ; even in our own- 

 generation so much has been accomplished that the hope may be 

 indulged of at last learning something of the history of these 

 earliest ages, when the earth had but lately ceased to glow, and 

 when the mystery of life began. 



THE LADIES' CONVERSAZIONE OF THE 

 ROYAL SOCIETY. 



"T^HE Ladies' Conversazione oi the Royal Society took place 

 on the evening of June 15 last, and in every way was 

 a distinct success, the attendance being the greatest on record, 

 and all the available space both for the guests and exhibits 

 being fully occupied. The exhibits, although they included a 

 few that were shown at the last soiree, were for the most part 

 new, and the following is a brief summary of the most notice- 

 able of them : — 



Dr. H. Hicks, F.R.S., showed the remains of a mammoth 

 found in Endsleigh Street, in March last, at a depth of only 

 22 feet. The bones were of enormous proportions, and in their 

 proximity was discovered a tusk which was estimated to have 

 been 12 feet in length. 



A series of enlarged transparent sections of the fossil plants of 

 the Coal-measures were exhibited by Prof. W. C. Williamson,. 

 F.R.S. 



Most interesting weie the water-colour drawings of Greek 

 temples, &c., by Mr. F. C. Penrose, which illustrated his 

 current investigations on the astronomical orientation of ancient 

 Greek emples. The drawings included those of the Pro- 

 pylaea, the Temple of the Wingless Victory, Parthenon, west 

 and east fronts of the Parthenon, north portico of the Erech- 

 theum, east portico of the Theseum, and the Temple of Jupiter 

 Olympius. 



Mr. W. M. Flinders Petrie showed some excellent water- 



