378 NATURAL SCIENCE. Nov., 1893. 



Leicester, recording an independent observation of his own on a 

 coping at Leicester, showing a similar result, which he attributed to 

 alternate heating and cooling by ordinary changes of temperature. 

 The reason why this sort of expansion shows so much in terra-cotta 

 copings, is because the joints are made in cement, and the whole 

 becomes a long bar, alternately exposed to the vertical rays of the 

 sun and to the cold. 



Finally, Professor Le Conte seems to think that if expansion 

 produces mountain elevation, contraction should bring the strata 

 back again to the same level. This is a very common criticism with 

 my objectors, and is due to a misconception born of looking at things 

 in the gross — and, if I may venture to say it — in too formal a manner. 

 The reason why the strata on contraction do not go back to their original 

 form and level I have explained over and over again. It is this, no 

 force on earth can pull strata back that have once been folded. The 

 material by every expansion, however small, is pushed forward, and 

 accumulates mostly in folds, so that the mountain range is actually 

 piled up, by transfer of material from one locality to another, just as 

 much as if it had been done by means of navvies and wheelbarrows. 



To give another illustration, landslips are of frequent occurrence, 

 and have been seen, or their effects seen, by many. One of those 

 effects is to push up a fold, or pile up any loose materials, such as a 

 shore deposit, before it. One might as well expect this material to 

 go back again, and spread itself out over its old bed if the landslip 

 were removed, as to expect mountain strata to do it, whether piled up 

 by horizontal or cubical expansion, or pushed up laterally in any 

 other way. 



If thinkers would not concentrate their minds upon vertical 

 expansion to the exclusion of horizontal and cubical, they would, I think, 

 find no difficulty in understanding one of the leading ideas of my 

 theory. In consequence of the extended areas of the sediments 

 compared to their vertical thicknesses, horizontal expansion is 

 infinitely greater in its effect than vertical. 



When, however, all is said, there is no gainsaying the fact that 

 the Origin of Mountain Ranges is a subject involving intricate 

 reasoning, and cannot be disposed of by formal statements, however 

 clear ; for their clearness frequently arises from the exclusion of 

 conditions which ought to be considered. 



My object in making these explanations and criticisms is entirely 

 to further the cause of a science which I have deeply at heart, and 

 which, for its progress, is dependent on the labour of many. No one 

 can rejoice more than I do at the valuable contribution towards 

 the elucidation of so difficult a subject as the Genesis of Mountain 

 Ranges with which the veteran Le Conte has favoured us. 



T. Mellard Reade. 



