0. Fisher — On Possible Changes of Latitude. 551 



Warminster. For tlie fossils of the " Meule de Bracquegnies," so 

 many of which have been referred by MM. Cornet and Briart to 

 Blackdown species,^ appear to me to form rather the passage fauna 

 between the (in England) totally distinct faunas of Blackdown and 

 Warminster. 



While thus maintaining the correctness of correlating beds 10 to 

 12 and the Warminster beds of Chute Farm with the Chloritic Marl 

 of Ibbetson, and of distinguishing all alike from the Upper Green- 

 sand, I ought at the same time to admit that such an arrangement 

 still leaves much to be more fully determined. Beds 10 to 12 and 

 the Warminster beds will still, to some extent, represent an un- 

 known quantity, inasmuch as they themselves include beds of 

 various ages, partly remanie, and which are probably elsewhere very 

 differently represented. Judged by their fauna they include certainly 

 two, if not three, divisions of the French and Belgian " Tourtias," 

 as defined by MM. Dumont, Cornet and Briart, Hebert, Gosselet, 

 Barrois, — and in part also the " Griinsand (Tourtia) von Essen." 

 Fragmentary beds all of them, existing often only as outliers, and 

 the exact correlation of which even Barrois ^ finds yet difficult to 

 determine. 



IV. — On the Possibility op Changes in the Latitudes of Places 

 ON the Earth's Surface ; being a Eeplt to Mr. Hill's 

 Letter. 



By 0. FisHEB, Clk., M.A., F.G.S. 



AM grateful to Mr. Hill for noticing my former paper "On 

 Possible Changes of Latitude on the Earth's Surface " in his 

 letter, October, 1878, p. 479. I wish, however, that he had gone into 

 the subject more in detail ; in which case I, and perhaps others, would 

 have felt more satisfied with his reply. He epitomizes my appeal to 

 physicists by making me ask, " Assuming that a thin crust surrounds 

 a fluid substratum, could then a deformation shift the crust over 

 the nucleus ? " And he replies that, Mr. G. Darwin having proved 

 that the earth is "enormously stiff," the discussion would be fruitless. 

 But in this statement of my question and reply to it, he has omitted 

 what seems to me the important proviso, based on Hopkins' reason- 

 ing about the mode of cooling, that this fluid substratum is shallow, 

 and encloses a rigid nucleus ; and given no reply to my inquiry 

 whether such a supposition might not afford the required rigidity. 



Again, referring to the recent disproof of Hopkins' demonstration 

 of rigidity drawn from the amount of precession, Mr. Hill argues 

 that, since the fluid nucleus being spheroidal and rotating would 

 resist the tilting force which produces precession, and the shell 

 would not slide freely, " would it not also resist the tilting tendency 

 resulting from a deformation ? " I am not quite certain that I under- 

 stand this. If Mr. Hill means that the rotation would compel the 

 fluid substratum to retain its spheroidal form, so that a rigid crust 



1 Briart et Cornet, Memoires de TAcademie R. de Belgique, torn. xxxiv._ 



2 Mem. sur le Terrain Cretace des Ardennes, etc., par Chas. Barrois, D.Sc, 

 Lille, 1878, p. 346. 



