136 



GLACIAL EPOCH. 



[Cf. XI. 



Fig. 125 



Fig. 126. 



Hycena spelcea; second molar, 

 left side, lower jaw; nat. size. 

 Cave of Kirkdale. Post-plio- 

 cene. 



Teeth of a new species of Articola, field-mouse; from 



the Norwich Crag. Newer Pliocene. 



a. Grinding surface. 5. Side view of same. 



c. Nat. size of a and b. 



Fig. 127. 



Fourth molar, right side, lower jaw. Ifegatlierium ; Geor- 

 gia, U. S. ; one-third nat. size. Post-pliocene. 



b. Crown of same. 



CHAPTER XL 



POST-PLIOCENE PERIOD CONTINUED. GLACIAL EPOCH. 



Geographical distribution, form, and .characters of glacial drift — Fundamental rocks, 

 polished, grooved, and scratched — Abrading and striating action of glaciers — 

 Moraines, erratic blocks, and " Eoches Moutonnees " — Alpine blocks on the Jura 

 — Colossal size of ancient Swiss glaciers — Continental ice of Greenland — Ancient 

 centres of the dispersion of erratics — Transportation of drift by floating ice- 

 bergs — Bed of the sea furrowed and polished by the running aground of floating 

 ice-islands — How to distinguish glacial drift of submarine from that of terrestrial 

 origin. 



Among the different kinds of alluvium described in Chapter VII., 

 a passing allusion was made (page 80) to the " boulder formation " 

 and to its origin as probably connected with the agency of glaciers 

 and floating ice. This formation, to which many names, such as 

 "diluvium," "northern drift," "boulder clay," and "glacial deposits" 

 have been given, is abundant in Europe north of the 50th, and in 

 North America north of the 40th parallel of latitude. It is wanting 

 in the warmer and equatorial regions, and reappears when we ex- 

 amine the lands which lie south of the 40th and 50th parallels in the 

 Southern Hemisphere; as, for example, in Patagonia, Terra del 

 Fuego, and New Zealand. It consists of sand and clay, sometimes 

 stratified, but often wholly devoid of stratification for a depth of 50, 

 100, or even a greater number of feet. To this unstratified form of 



