866 Marvels of the Universe 
forty-five miles. Roughly 
speaking, we may say that we 
live on a thin crust which is 
about one two-hundredth of 
the earth’s radius. As to 
what supports that crust, a 
great change has come over 
the views of the scientific 
world in recent years. Con- 
— — siderable light has been shed 
eee ee — upon this subject by obser- 
vation of the paths of waves 
set about by earthquake 
shocks. It is undoubtedly a 
fact that the centre of the 
earth contains a solid core of 
ie: = = heavy metal, possibly to a 
Photo bu] a LH. J. Shepstone. great extent nickel-iron, such 
Ayn cl Tine cf coxa os Wade Riza, from oltidh dhe oa leo Ikan as is found in meteorites, but 
lines ucliiesh from the manner in which 
shocks lose their velocity therein, or even are completely lost, it is possible that the real centre is of 
some less-conducting material, and this centre may be as much as two-fifths of the whole radius of 
the globe. But above the metal sphere, the ‘‘ barysphere,” there is room for that mass of highly- 
heated, molten material which finds its way at times to the surface through the weak places in the 
crust which give rise to volcanoes. 
So, then, at all events the crust is not so very thick after all. There is one central fact which 
seems to be retarding the thickening of the crust. Whatever may have been the extent to which 
heat may have been radiated 
into space in the ages that are 
gone, it is an undoubted fact 
that radium and its allies are 
now making up for any loss 
which the earth may be now 
suffering. We have it on 
good authority that below 
forty-five miles there is no 
radium; and as_ nickel-iron 
meteorites contain no radium, 
it is possible that here we 
begin to come within the 
range of accumulated masses 
of melted meteoritic matter. 
But the radium which is found 
in our thin crust is, in the 
opinion of some of the best 
authorities, sufficient to make 
Photo by] [R. Welch. 
up for the loss of heat which 
Tops of five-sided and six-sided columns, forming a portion of the Giant’s Cause- 
the goes on by radiation. In fact, 
way, Antrim. The rock is igneous dolerite. The concave tops of some of 
columns act as salt-evaporating pans. A state of equilibrium has been 
