[ 426 ] 



LV. On the Change in the Obliquity of the Ecliptic, its Influ- 

 ence on the Climate of the Polar Regions and on the Level of the 

 Sea. By James Croll*. 



IT is now pretty generally admitted by geologists that during 

 the past geological history of our globe the northern hemi- 

 sphere at least has passed through several glacial epochs. The 

 existence of an ice-period during the Permian and Upper 

 Miocene epochs, and perhaps during the Middle Eocene also, 

 may now be regarded as established-)-. And I believe that there are 

 few? geologists who have given special attention to the matter who 

 will not admit that we have evidence of the existence of ice-action 

 during the Silurian, Old Red Sandstone, and Cretaceous periods. 

 But what is most remarkable is the fact that during those very 

 same periods we have evidence of the existence of a much warmer 

 and more equable condition of climate than prevails at present. 

 And we have also indisputable evidence that this warm and 

 equable condition of climate was not confined to temperate re- 

 gions, but extended beyond the arctic circle, even up to the high- 

 est latitudes that man has yet been able to reach. I shall state 

 briefly a few of the facts to which I allude. 



In the arctic regions encrinites, corals, ''and mollusca be- 

 longing to the Silurian period have been found in abundance J, 

 proving that a warm sea must have prevailed in those regions 

 during at least a part of that age. It is well known that all over 

 the arctic regions, extending to the most northern limit that has 

 yet been attained, coal and carboniferous limestone have been 

 found in abundance. And the existence of magnesian limestone 

 in high latitudes seems to indicate that also during a part of the 

 Permian period a warm sea must have reached to arctic regions. 



We have evidence of a warm condition of climate in North 

 Greenland during the Oolitic period. For example, in Prince 

 Patrick's Island, at Wilkie Point, in lat. 76° 20' N. and long. 

 117° 20' W., oolitic rocks containing an ammonite (Ammonites 

 M'Clintocki, Haughton) like the Ammonites concavus and other 

 shells of the oolitic species were found by Captain M f Clintock§. 

 In Katmai Bay near Behring's Straits the following oolitic fos- 

 sils were found : — Ammonites Wossnessenskii, Ammonites biplex, 

 Belemnites paocillosus, and Unio liassinus || . Sir E. Belcher found 



* Read before the Geological Society of Glasgow, April 18, 1867, and 

 reprinted, by the permission of the Council, from tbeir * Transactions/ 

 vol. ii. part 3. 



t LyelFs * Principles,' new edition, vol. i. chap. x. and xi. 



X Quart. Journ. Geol. Soc. vol. xi. p. 510. 



§ Journal of the Royal Dublin Society for February 1857. 



|| Quart. Journ. Geol. Soc. vol. xi. p. 519. 



