26 =T. M. Reade—Hffects of Temperature on Terra- Cotta. 
where any considerable section of Chalk is exposed, as in a rail or 
road cutting, indicates natural subsidences whose origin may be 
traced to causes similar to those at Ripon. 
If it were possible to see the surface of the Chalk, bared of its 
superficial covering of clay, loam, etc., it would, I imagine, be 
singularly convex and concave. In digging pits, the chalk is 
is sometimes found close to the surface at one side of the shaft, but 
cannot be found at twenty or even thirty feet on the other side. 
V.—Errects or ALTERNATIONS OF TEMPERATURE ON TERRA CorTa 
CopINGs SET IN OxMENT AS AN ILLUSTRATION OF A THEORY OF 
Mountain Bouruprina. 
T. Mretuarp Reape, C.E., F.G.8., F.R.1.B.A. 
LSEWHERE I have shown that metals under certain conditions 
when subjected to changes of temperature undergo permanent 
deformation. Thus sheets of lead ridge up and fold even under the 
influence of atmospheric changes, as may be seen by the examina- 
tion of any old lead flats or cutters. The cumulative effect of small 
but repeated changes of temperature is very striking, and I have 
used it in illustration of what I conceive to be the true explanation 
of the ridgings up of the earth’s crust called mountain ranges. The 
examples given’ of the effects of alternations of temperature are 
mostly in metals, but I have also shown that other materials not 
ductile are affected in the same way, in a lesser degree. 
A very remarkable example has lately come under my notice? of 
the lengthening of a terra cotta coping, which it appears to me can 
only be explained on the same principle. 
The coping in question which, is freely exposed to the direct rays 
of the sun, consists of two courses of red Ruabon terra cotta bricks 
set in cement upon a fence wall, built with common bricks in mortar 
a brick and a half thick. The courses are level, but, in consequence 
of the inclination of the road, the coping is stepped down at intervals, 
so that the under-course of bricks of one length is just gripped and 
held in position by the top course of the next length of coping. It 
will thus be seen that it must constitute by liability to lifting a more 
delicate test than ordinary of any increase of length that might take 
place in the coping. 
When I examined the coping—and I have looked at it over and 
over again—the end portion of one length abutting against the next 
length at the drop in the level was thrown up into an anticlinal of 
about 6 ft. span ; the coping bricks being lifted in the highest part 
one inch from their bed. There was a fracture at the crown of the 
anticlinal, and another at the foot or springing, but for a distance 
of 30 feet the coping was practically one solid continuous bar. A 
careful examination showed that the coping had “ grown” about 
a quarter of an inch longer than when it was first set, and that this 
' Origin of Mountain Ranges, chap. iii. and iv. 
2 T am indebted to Mr. F. Archer for first calling my attention to it. 
