J. F. CAMPBELL ON GLACIAL PERIODS, 99 
of a journey round the North Cape, through Archangel and Astra- 
khan and the Caucasus, and round the south of Europe. In 1873 I 
followed the tracks of polar ice from the Arctic basin southwards till 
I lost the track in Russia. 9. In March 1876, a paper about the 
Period of Polar Glaciation was published in my ‘ Circular Notes,’ 
2 vols. It stated an opinion founded upon much study and obser- 
vation during thirty-five years after seeking for marks of polar 
glaciation round the world. In July 1874 I set out with this pro- 
position, “ Jf an Ice-cap ever existed, marks of it ought to be found on 
all meridians ;” upon facts observed in a year I founded an opinion 
in July 1875 and published it. 10. In July 1876, a paper about 
firths, dales, lakes, and caions was published in ‘ Nature” 11. In 
September 1876 wishing to test these, my opinions, in the Hima- 
layas, I started for India. After hunting over a country selected 
by myself with the counsel of Mr. H. B. Medlicott, in charge of the 
Indian Geological Survey, I wrote letters which were published by 
the Asiatic Society of Bengal. 12. The following paper contains 
opinions based chiefly on my own observations and facts, and on 
studies since I left school, after spending nearly six months in India 
and some weeks in Lombardy, and after crossing about 180° of lon- 
gitude on the journey out and home. 13. For some of the observed 
facts on which my opinion is based, I beg to refer to the publications 
above mentioned and to this paper. I have a great many rubbings 
taken from glaciated rock-surfaces to show the directions in which 
ice moved, and many other records of observations on a collection of 
maps, in manuscript journals, and stored otherwise. I write this to 
give grounds for stating the opinion of an amateur upon a large geo-~ 
logical question, which must be answered by facts. 
Il. Introductory. 
14. I may say in a few words what my facts seem to teach. I 
have learned to think of this world as a very little place. It is re- 
presented in the Museum of Practical Geology by a grain of small 
shot distant some yards from a 12-inch shell, with grains of snipe- 
dust and larger numbers to represent moons, planets, and a solar 
system on a comprehensible scale of distance and size. I have 
crossed the Arctic circle fourteen times, the tropic of Cancer four 
times, the equator twice, 360° of longitude in travelling round 
the world, and in 1876-77 a quarter of a circle of longitude thrice, 
I have shaken off childish ideas of vastness and unattainable dis- 
tances which hamper geological thought. I have learned to think 
of dimensions to scale; of geography as it is taught on a school globe, 
not as distorted in Mercator’s ‘ Projection ;’? of the world as a 
heated ball moving in space, which space, according to astronomers, 
is cold enough to keep water solid, but a ball so warmed from 
without by the sun’s rays as to keep water generally between 
90° and freezing, between evaporation, condensation, and solidity, 
as steam, vapour, water, and ice. The materials of which the world 
is made are governed by laws which apply to them in all quantities, 
small and great. Gases, vapours, and fluids vary in weight and 
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