76 Reviews — Dr. B. N. Peach's Higher Crustacea 



!N^ovembei' number of this Magazine (1908) was to caution geologists 

 not to push their new-born views too far in trying to account for 

 structural difficulties by overthrusts. It must be remembered that 

 the Moine thrust-plane has been proved to no more than 10 miles 

 overlap, but may, of course, be much more. Incidentally, I thought 

 the paper likely to elicit a correspondence helping the interpretation 

 of the phenomena of overthrusts. 



Perhaps the following considerations may be helpful to those 

 geologists interested in the subject. 



It may be contended that the Alps, having been compressed, 

 according to Heim, 78 miles, have been moved that distance over the 

 underlying rocks, and that therefore the power exerted to obtain that 

 effect is even greater than is required to create a thrust-plane such 

 as I have postulated, viz. 100 X 100 miles. Mountain building, 

 I contend, is not a parallel phenomenon, the building going on in 

 sections, and the mountain range being as it were modelled by the 

 pressure applied at different times in different localities, not by one 

 general movement. Internal variable strains are continually taking 

 place, and it is to these that the mobility seen in mountain structure 

 is due. The very name ' building ' is suggestive of the process of 

 addition, or brick on brick erection, Nature being both architect and 

 builder. It may be seen from this that the repeated pressures applied 

 in sections may have a general cumulative effect and constitute yet 

 another of those examples so often seen in nature where enormous 

 results arise from the repeated application of small forces. If it 

 could be demonstrated how fracture could have arisen by the 

 cumulative effect of small agencies, it would bring us nearer to belief 

 in the theory that transference of enormous masses of rock has been 

 effected b}' overthrusts. 



Mr. Fisher has ably restated his well-known theorj^ of convection 

 currents in the earth's interior. It seems, however, to me to be one 

 unlikely to provide the lateral pressure in the form and amount wanted 

 to create a thrust-plane. 



li E "V I E -W S 



I. — Monograph on the Highee, Crustacea, of the Caebonifkrous 

 EocKs OP Scotland. By B. N. Peach, LL.D., E.R.S., A.E.S.M. 

 Memoirs of the Geological Survey of Great Britain : Palaeontology. 

 4to; pp. 82, 12 pis. 1908. 



THERE is perhaps no group of fossil Crustacea of which the study 

 promises more important results for morphology and phylogeny 

 than does that of the primitive Malacostraca of the later Palaeozoic 

 periods. There is reason to hope that it may yet be possible to trace 

 among them the differentiation of some of the existing orders from 

 the common stock of the Malacostraca. Dr. B. T^. Peach published 

 important memoirs on the higher Crustacea of the Scottish Carboniferous 

 rocks nearly thirty years ago,^ and since his retirement from the service 



1 See B. N. Peach, Traus. Eoy. Soc. Edinb., 1882 & 1883, toI. xxx, etc. 



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