T. Mellard Readc — Mountain-Building. 351 



V. — Change of Form by Expansion as an Element in 

 Mountain-Building. 



By T. Mellard Reade, C.E., F.G.S., etc. 



SOME critics of my theory of the "Origin of Mountain Ranges" 

 appear to have strangely lost sight of one of the essential prin- 

 ciples upon which it rests. This seems to have arisen through their 

 attention having been too much engrossed with what I have said on 

 the subject of cubical or voluminal expansion. 



In my original work it was shown that the calculations of the 

 earlier investigators on the vertical lifting of a given thickness and 

 area of the earth's crust, by a given rise of temperature, must be 

 multiplied by three to arrive at a correct result, as they omitted to 

 consider the expansion in two horizontal directions at right angles to 

 each other, confining their attention to linear expansion in a vertical 

 direction. But, while calling attention to this oversight, it was certainly 

 not my contention that expansion would affect the earth's crust like the 

 expansion of water in an inexpansible vessel. 



The effect of expansion on a solid body like the earth's crust by 

 differential heating is to set up stresses and strains which relieve 

 themselves in the direction of least resistance, and in doing this an 

 internal movement and change of form ensue. A change of volume 

 of a section of the earth's crust therefore involves internal movement, 

 distortion, and change of form. 



This principle I illustrated by experiments on the ridging up pro- 

 duced by heating sheets of lead ; by the distortion of a sheet of zinc 

 and iron, rivetted together, and placed in an ordinary oven ; by the 

 well-known wrinkles and folds that occur in lead gutters, lead-lined 

 baths and sinks ; and since, by the permanent expansion which 

 frequently takes place in terra-cotta copings of walls through 

 differential heating by the sun's rays. 1 I could add considerably to 

 this list, but it is sufficient for my present purpose. The ridgings 

 up and distortions were shown in all these cases to be the cumulative 

 result of compressions and tensions set up by successive expansions 

 and contractions, due to alternations of temperature, ending in a 

 permanent extension in the case of a sheet, which is compensated for 

 by folds or wrinkles, or in the case of a bar by lengthening. 



Applying this principle to the probable effect of changes of tem- 

 perature in the earth's crust, I showed that the strata of which 

 mountain chains are composed have a wide areal extension, as in the 

 plains of Russia, which are composed of the Silurian and other rocks 

 involved in the Ural uplift. The same principle was shown to hold 

 true with the Appalachians ; and later, in this Magazine, I have called 

 attention to British geology as teaching us a similar truth. - These 

 strata out of which mountain ranges are evolved may be considered 

 as wide and extended sheets almost paralleled on a small scale, 

 excepting for the variable thickness distinguishing geologic deposits, 

 by the sheets I experimented upon. 



1 Geol. Mag , Dec. Ill, Vol. V, pp. 26, 27. 



2 Geol. Mag., Dec. IV, Vol. II, pp. 557-565. 



