November 21, 1918] 



NATURE 



235 



13,000 ft. or more ol clays, sandstone, and con- 

 glomerate, i> regarded a> ol lacustrine origin; and 



the upper, 21 Ft. ol massive conglomerates, as tor- 

 rential. The oil is found in the lower Fars group, 

 the detrital limestones forming the reservoir; at 

 Maidan-i-Naftun the wells all Bow undei strong pres- 

 sure, and a ears oi remarkable production 



show ni xhaustion. 



The geological history of the region seems to be 

 one of extraordinary interest. The strata, from tin- 

 base to the top of the Fars series, were deposited 

 in a qui. sc< nl basin, and the thickness of beds betwe< n 

 nt horizons remains very constant. At the 

 close of the Fars period folding began; the strata 

 were thrown into open folds, and the overlying 

 Bakhtiari serii s varies greatly in thickness, being 

 thickest in the synclines, and leasl over the anticlines; 

 towards the close of the period the synclines became 

 filled up with sediment, and the upper Bakhtiari con- 

 gloni' d over the whole. Then, according 



to the authors, a series of earth movements set in, 

 continuing to the present and giving rise to a very 

 complicated series of structures; fan, or, as they call 

 it, Omega, structure was developed, and a series of 

 thrust-faults which cam ■ right up to the surface and 

 were partly determined bj accidents of surface relief. 

 In some cases the folds are completely overlaid by 

 one overthrust extending beyond the next, and at 

 Maidan-i-Naftun this is said to have been prevented 

 only bv the action of the Karun River, which flows 

 for some miles in a gorge Soo ft . deep between the 

 Tembi thrust-fault, which hades towards the oilfield 

 on one side, and the back fault of the next fold, 

 which hades in the opposite direction. The authors 

 believe, in short, that the faulting and folding -of this 

 region were not only superficial, but also of recent 

 date .uid continued, with a gradual relaxation, to the 

 present day; they regard the surface features as 

 dui to the movements caused, to some extent, 

 as determining this faulting, and consider that the 

 ' advancing fronts of the overthrust blocks have been 

 worn away by surface denudation, concomitantly with 

 their advance bv the action of the tectonic processes. 



The Ahwaz-Pusht-i-Kuh region presents much the 

 same features, with less intense disturbance; but in 

 Qishm Island the identification of the rock series 

 with that of the Bakhtiari country is doubtful, and 

 the structure is very different, the rocks being dis- 

 posed in a series of gentle domes along an axis 

 running through the length of the island, these domes 

 being subsidiary to a larger dome, exposing an inlier 

 of the Focenc Hormuz series. Four explanations of 

 this dome are discussed : that it is due to the inter- 

 s' ction of two open folds of different dates, that it is 

 of the same nature as the salt domes of Texas, that 

 it is due to a laccolitic intrusion, and that it is due 

 to the compression of the softer Miocene strata against 

 a pre-existing boss of Forene, round and against which 

 they were deposited. No opinion is offered as to the 

 relative probability of these, but the general features 

 seem more in consonance with some cause analogous 

 to the second and third, though the material to which 

 the local uplift was due may have been neither salt 

 nor a nlutonic intrusion. Neither this nor the Ahwaz- 

 Pusht-i-Kuh district has proved oil-bearing in. a com- 

 mercial sense, though indications have been found 

 and both arf> being tested. 



We may express a hope that, the absolute em- 

 bargo on publication having been lifted, more of the 

 large amount of geological information which is in 

 possession of the Anglo-Persian Oil Co. and of the 

 Indian Government may be made accessible. There 

 can be no commercial reason for secrecy, as the com- 

 pany has a monnnr.lv of the whole country, and the 



NO. 2s6o. VOL. I02] 



political reasons have been largely, and ma) soon be 

 completely, removed. The value of publication will 

 be great, as the region is one of extraordinary interest 

 both in its structural aspect and as regards it's bearing 

 on the principles which underlie the origin and dis- 

 tribution of peti oleum. 



THE CONSTITl HON OF THE EARTH'S 



EXTERIOR. 1 

 'T'HE problems of the interior of the earth are 

 -*• primarily of a physical character, and, in the 

 final appeal, only to be decided by mathematical treat- 

 ment ; but this, in its turn, must be based on observa- 

 tion, and, therefore, it comes that this discussion is 

 prefaced by a statement of the results which have 

 been obtained by the sciences of observation. The 

 ration of this statement is simplified by the fact 

 that the problems fall naturally into two tolerably 

 distinct groups : (1) those relating to the outermost 

 layer, amounting at most to 1 per cent, of the radius, 

 and (2) those of the deeper portions, extending to the 

 centre. 



The latter may be taken first. Records of the 

 transmission of mass waves set up in connection with 

 earthquakes show two well-marked groups repre- 

 senting two forms of wave-motion, presumably the 

 longitudinal and transverse, and a steady increase of 

 the rate of transmission, with no very marked break 

 in regularity, up to a distance of about 120 from the 

 origin. Beyond that the first phase, of longitudinal 

 waves, shows a decrease in velocity, and the second 

 phase, of transverse waves, which, though so con- 

 spicuous at lesser distances, are no longer represented 

 in their typical form, but are replaced by a record of 

 different character, probably not due to anv form of 

 wave which has followed the direct path from the 

 origin, and markedly delayed from the time at which 

 they should have arrived had the same relative rate of 

 propagation been maintained as at lesser distances. 

 The depth reached by waves emerging at 120 from 

 the origin is about half the radius from the centre of 

 the earth, and the conclusion to be drawn is that 

 down to that depth the material of which the earth 

 is composed is sufficiently rigid against stresses of 

 short duration, and sufficiently isotropic to permit the 

 transmission of the two forms of elastic waves and 

 to give rise to their separation by reason of the 

 different rates of travel. Further, it seems that down 

 to a depth of half the radius there is no marked 

 change in the character of the material, but at greater 

 depths there is a change in phvsical character to a 

 material, or form of matter, which is no longer able 

 to transmit the distortional waves, or, if capable, can 

 onlv do so with a great diminution of intensity and 

 at about half the rate in the lower layers of the outer 

 shell ; in other words, the material in the central 

 nucleus has a very low degree of rigiditv, even against 

 stresses of onlv a few seconds' duration. The limit 

 between the central nucleus and outer shell lies 

 between four-tenths and five-tenths of the radius, 

 measured from the centre of the earth ; the transition 

 hetwpen the two is apparently gradual, and not suffi- 

 cientlv abrupt to give rise to reflection of the waves 

 at the iunction of the two. 



Turning to the outer layers, we have, next the sur- 

 face, partly material which has been disintegrated bv 

 the processes of surface denudation, transported, 

 deposited, and resolidified, and partly rock which has 

 not undergone these processes, but is thoroughly 

 cooled and solid in everv sense of the word. These 



1 Synopsis of the opening of a discussion at a meetine of the British 

 al Committee on November 10, by R. D. Oldham, 

 F.RS. 



