306 GEOLOGY, 



Even in Arctic regions there are many evidences of the prevalence 

 at different times in the past of temperate and even semi-tropical 

 climates. In Grinnell Land Dr. Hayes obtained corals and cham- 

 bered shells, which indicate that warm oceans once obtained there. 

 The adjoining lands at the same time nourished a most luxuriant 

 vegetation. We have seen that in our own State there have been, 

 even in Cenozoic times, semi-tropical conditions, which very grad- 

 ually disappeared and gave place to Arctic and again to warm, 

 temperate climates. It is a fact, therefore, that climates rotate 

 throughout the geologic ages. The old idea that the earlier warm 

 climates were produced mainly by the then higher temperature of 

 the interior of the globe, and that the colder modern conditions 

 have been brought about principally by gradual cooling of its mass, 

 is now almost universally abandoned. The earth still radiates heat, 

 as it always has done, but its effects are not now — and it is doubtful 

 whether, during recorded geological time, it has been perceptible. 

 In all times climates have varied in proportion to the heat which 

 the globe received, directly or indirectly, from the sun. Even in 

 the Silurian the climates were probably as well marked as now. 

 The question then eventually rises, what is it that causes the varia- 

 tions in the climates of the globe? My limits only permit me to 

 refer to those explanations that have received the most attention, 

 and which, in my judgment, are the most probable. 



The theory accounting for climatic changes which has been sanc- 

 tioned by the greatest number of geologists during this generation 

 was proposed and defended by that prince among naturalists, Lyell. 

 He referred to the admitted fact that through the geological ages sea 

 and land have many times changed places — that it is hard to find a 

 place where the billows of the ocean did not formerly roll — that all 

 the strata formed since the opening Laurentian arc only so many 

 fossil sea bottoms. Even now some coast lines are sinking and 

 others are rising, and a continuation of these changes will engulf 

 some existing lands and raise some sea bottoms above the water. 

 Even the relative levels of closely-joining land masses slowly change 

 in this way. When, therefore, we are required by Lyell's theory 

 to believe that the relative distribution of land and water was form- 

 erly very different from what it is now, no one questions the facts 

 on which this theory is based. If now such changes were brought 

 about that the principal land masses should be placed in equatorial 

 regions, the mean temperature of such high northern lands as were 



