Cause of the Glacial. Period 
machina such as the theory of cold and warm regions in space, or such slow-working agencies as the varying eccentricity 
of the earth’s orbit, a theory whose very supporters admit could only have produced the required effects if favoured by 
other exceptionally propitious circumstances. 
The late Cavaliere W. P. Jervis, F.G.S., Conservator of the Royal Italian Industrial Museum at 
Turin, writes :— 
Few geological difficulties have constantly presented themselves to my mind of such a serious kind as the 
explanations advanced as to the causes of changes of climate on our globe in geological times, including the intense 
cold during the Glacial epoch, and the converse warmer temperature during the Miocene epoch. None of the theories 
elicited have convinced me. But the paper read before the Victoria Institute by Professor Hull, based, as the 
arguments are, on the most forcible logical and palaeontological data relating to the entire eastern and southern 
coast-lines of North America, has dissipated, as by enchantment, all my doubts ; and the proofs he adduces of the 
former non-existence of the Gulf Stream appear to me to throw a bright light upon many obscure points of geological 
climatology. bd : 
Though Lyell laid great stress upon changes in the geographical configuration of our globe at successive periods 
of its existence, and showed the ever-changing elevation and depression of vast tracts of country, it would appear that 
enough attention has not been paid to these considerations, and hypothetical astronomical causes have found too much 
favour with not a few geologists—and in absence of proofs. 
River-valleys have been plainly traced by Issel to great depths in the Mediterranean, in prolongation of what are 
now short valleys in Northern Italy, and doubtless elsewhere much progress will be obtained in our knowledge of the 
past, of the fauna and flora of geological epochs, and of the erstwhile distributions of land and water, by a more 
extensive study of soundings of the ocean.! 
Professor Cooke describes the abundant fossil remains of elephants which he found in Malta, and draws from this 
fact, as also from the existence of like fossil bones in Sicily, the conclusion that these islands once formed part of the 
African Continent, previous to a considerable submersion of land now constituting deep sea. 
Professor Hull beautifully explains how we can find Arctic forms of marine molluscs in rocks not so far from 
London, and proves the possibility of there having once been extensive glaciers on loftier mountains in Scotland, and 
of which we still find the traces. 
Will the Professor permit me to suggest that it would be a most important point, in order to corroborate his 
views regarding the assumption of a mean lower temperature of 10° F. previous to the formation of the Gulf Stream, 
to take accurately into account the longitudinal breadth of the Atlantic previous to the submergence of the Continental 
Shelf and of the Blake Plateau, i.e. during the Pliocene and Pleistocene epochs, by ascertaining whether there are 
corresponding proofs of submergence of the South American Continent, even of the African coast, for evidently she 
length of time the superficial ocean current was subject to the rays of a tropical sun would have an effect analogous 
to what takes place now in the Gulf of Mexico? 
Professor Hull’s able paper is calculated to open out a vast field of important geological investigations. The 
depression of the Atlantic coasts of North America and of North-Western Europe has no parallel in many parts of 
Western Africa. But changes of climate in a reverse direction after the Miocene epoch can be accounted for by the 
still later upheaval which has left the vast deserts of Northern Africa, Arabia, and Central Asia as clear proofs of the 
existence of former seas, permitting elephants to live in the long island of Morocco, Algeria, Tunisia, and Malta, and 
rendering the climate of Siberia milder than at present. 
Geology and physical geography are twin sisters ; their requirements are so intimately united that they cannot 
be too closely associated ; the opening or closing of sea communication between two points, as likewise changes in the 
elevation of land, finally deviations of ocean currents, materially alter the climate of the globe, irrespective of all extra 
terrestrial agencies. 
THE AUTHOR’S REPLY 
The general concurrence in my views, stated by Professor T. Rupert Jones, is a matter of much 
gratification. He has touched on one of the points referred to by Colonel Feilden above. 
1 One of the most interesting series of six maps exhibited by Dr. Gerard de Geer in the Swedish section of the VIth International Congress, 
held in London in 1896, showed the glacial regions of Finland and Scandinavia at different periods. In the first map he endeavoured to prove the 
existence of a continuous ice barrier from Greenland to St. Petersburg, coming down as far south as Denmark and North Germany. The next 
map showed the retreat of the limit of eternal snow and ice, the line passing through Central Sweden ; while in another map the glaciers were 
confined to certain mountainous tracts of Norway ; Sweden and Finland being out of the question. This is no mere conjecture. Professor 
Neovius, of Helsingfors University, in a prolonged conversation I had with him on this subject, declared that the deductions were founded on the 
geographical distribution of the granite ice-borne boulders abundantly found along more than 15° of longitude in consecutive order. 
I found that glacial boulders of Finnish granite were well known to exist in the neighbourhood of Halle, while I was engaged at work at 
Eisleben, but in Finland and Sweden the boulders are more common along the edge of the former isotherm of 32°. 
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