QUATERNARY AGE. — GLACIAL PERIOD. 541 



shed, in order that it may have sent a glacier over New England, 

 renders it probable, as stated on page 538, that part of this height was 

 acquired through an elevation of the land. It may be that the Great 

 Lakes were largely drained, in consequence of the lifting at the north. 1 



The view that the land of Great Britain was above its present level, 

 when the glacier was formed, is urged by Lyell, Dawkins, Geikie, and 

 other British geologists. Erdmann, in his elaborate memoir on the 

 Quaternary of Sweden, observes that the fact of elevation is established 

 by the extent to which rocks were polished beneath the sea level, and 

 that the country was probably so much raised that a large part of 

 the Baltic was dry land. Great Britain was probably at the same 

 time joined to Europe (p. 572), and to the islands on the north. Scot- 

 land, as its fiords and the channels between the Hebrides show, must 

 have been at least 1,000 feet above its present level. 



2. Source of the Cold. — The occurrence of an ice-period was 

 probably dependent mainly, as suggested by Lyell, on the extension 

 and elevation of the land over the higher latitudes. The movement 

 may have resulted in the closing of Behring Straits, — only 180 feet 

 deep, — and the connection of America and Europe across the Polar 

 Sea. In such a case, the tropical currents of both the Pacific and At- 

 lantic would have been confined to these oceans, instead of flowing into 

 the Arctic seas; and hence their ameliorating influence on the climate 

 of Northern Europe and America would have been lost, enhancing the 

 refrigerating effect of the high-latitude movement. Variations in the 

 degrees of cold, and in the amount of precipitated moisture, would 

 naturally have occurred at intervals in the course of the era of cold, 

 and have led to retreats and extensions of the glacier ice, and varia- 

 tions in the condition of some parts of the country invaded. 



Other sources of a cold climate have been appealed to. 



(1.) The diversion of the Gulf Stream over the submerged Isthmus of Panama into 

 the Pacific ; or else cutting off the South Atlantic supply, by a barrier made by the 

 elevation of the under-oceanic ridge between the east cape of South America and 

 Africa; — either is a hypothesis without facts or probabilities in its favor. It is certain 

 that, when the Champlain period opened, the Gulf Stream, as Verrill has remarked, had 

 its usual course; for, while the elevated sea-border Champlain formations north of Cape 

 Cod contain cold-water fossils, those of Nantucket, and other localities south of the 

 Cape, contain warm-water species, — and the same that now live on these coasts. 

 Hence, the currents flowed then as they do now. 



(2. ) The passing of the earth through one of its eras of maximum eccentricity of 

 orbit (see page 697): a cause that puts the Glacial periods of the Northern and South- 

 ern hemispheres not far from a hundred thousand years apart: at the time that it gave 

 increased cold and length to the Northern winters, it would give an equable climate 

 to the Southern hemisphere. The cause alone appears to be wholly inadequate; but 



1 The author's views on fiords and the subdivisions of the Quaternary (Post-ter- 

 tiary) were first published in the Amer. Jour. Scl., II. vii. 379, 1849, and xxii. 325, 346, 

 1856. The subject is further reviewed and extended in III. i. 1, ii. 233, 1871, and v. 

 198. 1873. 



