24 REPORT — 1886. 



Atlantic growth on modern geography. It has given na rugged and 

 broken shores composed of old rocks in the north, and newer formations 

 and softer features toward the south. It has given us marginal moun- 

 tain ridges and internal plateaus on both sides of the sea. It has pro- 

 duced certain curious and by no means accidental correspondences of the 

 eastern and western sides. Thus the solid basis on which the British 

 Islands stand may be compared with Newfoundland and Labrador, the 

 English Channel with the Gulf of St. Lawrence, the Bay of Biscay with 

 the Bay of Maine, Spain with the projection of the American land at 

 Cape Hatteras, the Mediterranean with the Gulf of Mexico. The special 

 conditions of deposition and plication necessary to these results, and their 

 bearing on the character and productions of the Atlantic basin, would 

 require a volume for their detailed elucidation. 



Thus far our discussion has been limited almost entirely to physical 

 causes and effects. If we now turn to the life-history of the Atlantic, 

 we are met at the threshold with the question of climate, not as a thing 

 fixed and immutable, but as changing from age to age in harmony with 

 geographical mutations, and producing long cosmic summers and winters 

 of alternate warmth and refrigeration. 



"We can scarcely doubt that the close connection of the Atlantic and 

 Arctic oceans is one factor in those remarkable vicissitudes of climate ex- 

 perienced by the former, and in which the Pacific area has also shared in 

 connection with the Antarctic Sea. No geological facts are indeed at first 

 sight more strange and inexplicable than the changes of climate in the 

 Atlantic area, even in comparatively modem periods. We know that in 

 the early Tertiary perpetual summer reigned as far north as the middle 

 of Greenland, and that in the Pleistocene the arctic cold advanced, until 

 an almost perennial winter prevailed, half-way to the equator. It is no 

 wonder that nearly every cause available in the heavens and the earth has 

 been invoked to account for these astounding facts. 



It will, I hope, meet with the approval of your veteran glaciologist 

 Dr. Crosskey, if, neglecting most of these theoretical views, I venture 

 to invite your attention in connection with this question chiefly to the old 

 Lyellian doctrine of the modification of climate by geographical changes. 

 Let us, at least, consider how much these are able to account for.' 



' The late Mr. Searles V. Wood, in an able summary of the possible causes of the 

 succession of cold and warm climates in the northern hemisphere, enumerates no 

 fewer than seven theories which have met with more or less acceptance. These are :^ 



1. The gradual cooling of the earth from a condition of original incandescence. 



2. Changes in the obliquity of the ecliptic. 



3. Changes in the position of the earth's axis of rotation. 



4. The effect of the precession of the equinoxes along with changes of the eccen- 

 tricity of the earth's orbit. 



5. Variations in the amount of heat given ofE by the sun. 



6. Differences in the temperature of portions of space passed through by the earth. 



7. Differences in the distribution of land and water in connection with the flow 

 of oceanic currents. 



