3884.] Construction of a Chapter in the History of the Earth. 197 



relationships they do. But this difficulty would not exist could we 

 suppose that what are now South Africa and India then lay on the same 

 side of the Equator ; and thus the palaeontology of these beds, as well as 

 their petrology, points towards the conclusion that in early Secondary 

 times the crust of the earth did not occupy the same position with respect 

 to the axis of rotation as it now does. 



That none of these arguments are conclusive by themselves I ad- 

 mit ; I willingly admit that the floras preserved to us represent but a 

 fraction of the species that lived when the beds that have yielded our 

 fossils were being deposited, but the probability is vastly against only 

 those species which were related to each other in the two countries 

 being preserved, and we may, I think, safely argue from the small sample 

 preserved to the larger bulk which is lost. In the same manner, I freely 

 admit that the differences in the severity of climate may have been due 

 to other causes besides difference of latitude, but on the average a colder 

 climate indicates a higher latitude, and, when we find that, from whatever 

 point we approach this matter, we are led towards the same conclusion, 

 it seems to me that there is a very strong presumption in favour of its 

 truth. 



I fear this paper has already extended to too great a length for 

 me to examine the arguments that have been put forward to prove that 

 any change of latitude is physically impossible, but I cannot conclude 

 without pointing out that what has been proved is that no conceivable 

 elevation or depression of the earth's surface could produce an appreci- 

 able alteration in the axis of rotation of the earth as a whole. But, though 

 the mathematical reasoning on which this conclusion is based may be 

 unassailable, it has no bearing on the question of whether changes of 

 latitude may not have taken place in the past, except on the assumption 

 that the earth is rigid throughout, and that the crust has no power of 

 sliding over the heated if solid core, an hypothesis which has been ably 

 combated by the Rev. 0. Fisher,* and which I hold to be inconsistent 

 with the known facts of stratigraphical geology. While, if the views 

 put forward in this paper are true, — and there seems to me a very strong 

 presumption in their favour, — the crust of the earth must in Mezozoic 

 times have occupied a very different position with reference to the axis of 

 rotation from that which it does at the present day. 



As yet the only fact which has in any material degree attracted the 

 attention of English geologists is the prevalence during the past of mild 

 climates within what are now the Arctic regions ; and hypotheses have been 

 broached to account for this independent of an alteration of the position 



* Physics of the Earth's Crust passim ; see particularly p. 184. 



