LITERARY NOTICES. 



267 



power and light. Within the past hundred 

 years the science of geology has sprung into 

 existence, and only about fifty years ago its 

 division known as glacial geology began with 

 the grand work of Agassiz in his study of 

 the glaciers in the Alps, of their former 

 extension across the wide valley of western 

 Switzerland to Mont Jura, and of the glacial 

 drift in Great Britain which he at once saw 

 to be due to the former presence of sheets of 

 land ice. At nearly the same time, in 1841, 

 Boucher de Perthes made the first collection 

 of stone implements in the gravel terraces of 

 the Somme Valley, by which geologists and 

 archaeologists were reluctantly convinced that 

 the human race dates back to a remote pre- 

 historic period, since which time very great 

 changes of climate have taken place and the 

 valleys of many rivers have been eroded far 

 below their old flood plains. Because of the 

 relationship of the earliest traces of man 

 with the Glacial period, this latest part of 

 the geologic record has attracted the interest 

 of many observers and nearly all readers; 

 new and important discoveries are being made 

 every year, and a vast amount of literature 

 in scientific journals and government reports 

 is constantly accumulating ; but many diffi- 

 cult problems in this field remain still under 

 discussion, concerning measurements of the 

 antiquity of man, the duration of post-glacial 

 time and of the Ice age, the causes of its 

 climatic changes, and whether it consisted of 

 only one epoch of glaciation or of two or 

 more separated by mild and warm interglacial 

 epochs when the ice-sheets were melted away. 

 Among these observers and writers none 

 during recent years has traveled more exten- 

 sively to gather information or been more 

 successful in contributing to our knowledge 

 than Prof. Wright, who in this book, as in 

 his previous larger volume, treats this sub- 

 ject in a clear, vigorous, and entertaining 

 style. 



Agassiz reasoned, from the action of the 

 Swiss glaciers in their wearing the rock sur- 

 faces over which they moved, and in their 

 transportation of drift and formation of 

 terminal moraines, that all countries bearing 

 such marks or striae on the bed-rocks and 

 similar deposits of till, or intermingled bowl- 

 ders, gravel, sand, and clay, have been over- 

 spread by ice. Prof. Wright similarly de- 

 votes fifty pages to descriptions of glaciers 



now existing, and of the ice-sheets of Green- 

 land and the Antarctic continent, before con- 

 sidering the evidences of past glaciation. On 

 the Sierra Nevada and Mount Shasta living 

 glaciers are found, but are of very small 

 size. Northward they occur in increasing 

 numbers and abundance on the Cascade 

 Range and in the Selkirk Mountains and the 

 Coast Ranges of British Columbia and Alaska. 

 About one hundred and fifty miles north of 

 Sitka the Muir Glacier, which was explored 

 and mapped by Prof. Wright in 1886, has 

 an extent of about three hundred and fifty 

 square miles ; and the Malaspina Glacier or 

 ice-sheet, lying between Mount St. Elias and 

 the ocean, mapped by Russell in 1890 and 

 1891, covers some fifteen hundred square 

 miles. These are very far surpassed, how- 

 ever, by the Greenland ice-sheet, explored by 

 Rink, Nordenskibld, Nansen, and Peary, 

 which probably has an area of half a million 

 square miles ; and the Antarctic ice-sheet is 

 ten times more extensive, occupying, indeed, 

 a somewhat greater area than the northern 

 half of North America, which was enveloped 

 by ice during the Glacial period. 



The terminal moraines of the ancient ice- 

 sheet of this continent have been traced by 

 Wright, Chamberlin, Salisbury, Leverett, 

 Upham, and others, from Nantucket and 

 Cape Cod, westward through Long Island, 

 northern New Jersey and Pennsylvania, Ohio, 

 and other States to Minnesota and North 

 Dakota ; and farther westward the glacial 

 boundary crosses Montana, Idaho, and Wash- 

 ington to the Pacific south of Vancouver 

 Island. Stone implements proving the pres- 

 ence of man here during the Ice age have 

 been found in plains and terraces of modi- 

 fied drift deposited in valleys by streams 

 flowing from the melting and receding ice- 

 sheet in New Jersey, Ohio, Indiana, and 

 Minnesota. Equal or greater antiquity must 

 be also affirmed for the Calaveras skull, 

 stone mortars, pestles, and spear-heads which 

 have been obtained by Whitney, King, Becker, 

 Wright, and others, from the gold-bearing 

 gravels under the lava of Table Mountain in 

 California. 



In the chapter on the ancient glaciers of 

 the Eastern hemisphere a very valuable con- 

 tribution of more than forty pages is from 

 the pen of Mr. Percy F. Kendall, relating to 

 the glaciation of the British Isles, with a map 



