25 



is but a vast collection of meteoric masses revolving rapidly- 

 round the sun, very near to its surface ; the fall of these 

 into the sun adds to its heat by the amount of sensible 

 motion arrested. In the great circle traversed by the sun there 

 will be blank spaces, where the supply of fresh fuel will be 

 deficient, and a diminution of its heat will produce a glacial 

 period. In other parts of its orbit the supply will be great, 

 and the consequent increase will produce a warm period. We 

 are at present enjoying one of the warmer periods, the mid- 

 summer of which may have been about the 11th century of 

 our era. For, since then, the glaciers of the Alps have been 

 slowly descending. In the 17th and 18th centuries they 

 stopped up roads formerly open, and covered forests of ancient 

 growth, and the early Arctic explorers found the Arctic Seas 

 much more free of ice than they are now. We are again 

 slowly approaching a cold period ; whether it may be equally 

 intense with the last one who can tell 1 



The effects of the last glacial period are clearly apparent in 

 the form of the surface in Northern Europe. Our rivers flow 

 through broad valleys that have been scoped out by ice ; our 

 lands have been covered with sediment, the grindings of the 

 rocks of ancient glaciers, which has given richness and fertility 

 to our vegetable soils. Lakes of exquisite beauty have been 

 hollowed out by the grinding power of ice, which now, filled with 

 water, are slowly silting up, yielding broad meadows on their 

 shores, and proving that liquid water was not the agent that 

 formed them. The gradual advance of living forms from the 

 lowest to the highest, which the rocks disclose, has probably 

 been greatly promoted by the constant change in the conditions 

 of life, which alternate cold and warm periods must have pro- 

 duced. Sir Charles Lyell has shown that man's existence on the 

 earth can be traced to the close of the glacial periods. If the 

 doctrine of the continuity of life, so ably advocated by the great 

 Darwin, and so well sustained by Mr. Grove, at the recent meet- 

 ing of the British Association, be true, then man's predecessors 

 must have existed through all that epoch. How the difficulties of 

 that period may have acted on his intellect it is very easy to see. 

 The necessity for shelter, for clothing, for mutual intercourse and 



