. Island life; or, the phenomena and causes of insular faunas and floras, including a revision and attempted solution of the problem of geological climates. , so that the only well-marked token of its presencewill be the larger masses of rock that may have been broughtdown. Such blocks are found abundantly in many of thedistricts of our ow^n country where other marks of glaciationexist, and they often rest on ridges or hillocks over which theice has passed, these elevations consisting sometimes of loosematerial and sometimes of rock different from that of vjhich theblocks are composed. These a
. Island life; or, the phenomena and causes of insular faunas and floras, including a revision and attempted solution of the problem of geological climates. , so that the only well-marked token of its presencewill be the larger masses of rock that may have been broughtdown. Such blocks are found abundantly in many of thedistricts of our ow^n country where other marks of glaciationexist, and they often rest on ridges or hillocks over which theice has passed, these elevations consisting sometimes of loosematerial and sometimes of rock different from that of vjhich theblocks are composed. These are called travelled blocks, and canalmost always be traced to their source in one of the highervalleys from which the glacier descended. Some of the most ?] THE GLACIAL EPOCH. 107 remarkable examples of such travelled blocks are to be found onthe southern slopes of the Jura. These consist of enormousangular blocks of granite, gneiss, and other crystalline rocks,quite fcreign to the Jura mountains, but exactly agreeing withthose of the Alpine range fifty miles away across the greatcentral valley of Switzerland. One of the largest of these blocks. MAP SHOWING THE COURSE OF THE ANCIENT GLACIER OF THE RHONE, AND THE PISTRIBITTIONOF ERRATIC BLOCKS ON THE JURA. is forty feet diameter, and is situated 000 feet above the level ofthe Lake of Neufchatel. These blocks have been proved bySwiss geologists to have been brought by the ancient glacier ofthe Rhone which w^as fed by the whole Alpine range from MontBlanc to the Furka Pass. This glacier must have been manythousand feet thick at the mouth of the Rhone valley near the 108 ISLAND LIFE. • [part i. head of the Lake of Geneva, since it spread over the whole ofthe great valley of Switzerland, extending from Geneva toNeufchatel, Berne, and Soleure, and even on the flanks of theJura, reached a maximum height of 2,015 feet above the numerous blocks scattered over the Jura for a distance ofabout a hundred miles vary consider
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