Notices of Memoirs — A Triassic Isopod Crustacean. 277 



Dr. Jeffreys takes this suggestion to be a fact, and would have us 

 believe that the thickness of this radio-active layer has been fairly 

 accurately measured and that consequently it is possible to calculate 

 the depth of the level of no strain. 



The discovery of radio-active elements in the rocks of the earth 

 has not rendered the compression theory any more probable. In its 

 naked simplicity it appears to show that the earth is getting hotter 

 and increasing in diameter at an "appalling rate". I am inclined 

 to agree with Holmes that the radio-active elements are mainly 

 concentrated near the earth's surface; but think that the exact 

 amount of concentration is uncertain. An expanding earth would 

 account for the formation of " rift valleys ", normal faults and lines 

 of volcanic activity or crustal weakness. 



The theory I have supported to the effect that the folding and 

 contortion of the rocks of the earth's crust have been largely due to 

 vertical flow resulting from denudation and horizontal flow by the 

 spreading of elevated areas, would account for the peculiarities our 

 rocks present even if the earth ivere sloivly expanding. 



Dr. Jeffreys states that " substances possessing any elasticity are 

 called solids". "If it is absent . . . the substance is a fluid." 

 Contrast this statement with the following from Maxwell's Theory 

 of Heat, edited by Lord Kayleigh, p. 302 : "Gases and liquids, and 

 perhaps most solids, are perfectly elastic, as regards stress uniform 

 in all directions, but no substance which has yet been tried is 

 perfectly elastic as regards shearing stress, except perhaps for 

 exceeding small values of the stress." Dr. Jeffreys will find that the 

 difference between a solid and a liquid is clearly stated on p. 303 of 

 the above quoted work. Both solids and liquids are brittle and 

 elastic. This can, in the case of a liquid, be clearly seen as regards 

 pitch, but not in the case of water; but all liquids are elastic even 

 under tangential stress. 



In my article on "Mountain Building" which Dr. Jeffreys 

 criticizes, I did not venture to introduce nny new theories concerning 

 the properties of matter, and I think that my critic should have 

 pointed out that his views are not those of our textbooks. To my 

 mind his theories concerning the solid and liquid states are quite 

 inadmissible. 



nsroTiCES o:f nvEEnycoii^s. 



A Triassic Isopod Ckustackan from Australia. 

 A Fossil Isopod bklonging to the Freshwater g'etsvs Phreatoicvs. 

 By Chas. Chilton. Journ. Proc. Hoy. Soc. N.S. "Wales, li, 

 pp. 365-88, 13 text-figs., 1918. 



OF the six (or perhaps seven) sub-orders composing the order 

 Isopoda, only the Flabellifera and Yalvif era have been definitely 

 recognized in a fossil state. The Flabellifera are represented b)' 

 several genera as early as the Jurassic, while the Yalvifera are known 

 only by a single species from the Oligocene. Professor C. Cliilton 

 now announces the discovery, in the supposed llhsetic rocks of New 



