2 20 JOURNAL OF SCIENCE. 



and of Kilimanjaro in Africa, are almost on the equator ; but there is 

 no well authenticated account of glaciers having existed in the tropics 

 during the pleistocene period. 



Ice-sheets are at present confined to polar regions, extending to 

 63° N. in Greenland and to 66° S. on the Antarctic continent. 

 During the pleistocene period an ice-sheet extended in North America 

 as far south as the junction of the Ohio with the Mississippi — in 

 37° 30' N., and in Europe to 50 u N. 



Shore-ice is found in high latitudes only. Coast-ice is broken up 

 into rafts or floes in summer, and these floes are often driven on 

 shore and piled up in gales of wind. 



Ice-bergs penetrate to about 40° N. and 40° S., but they are 

 isolated. Pack-ice, formed of united ice-bergs, occurs only in high 

 latitudes. It is often called Floe-berg. 



Ice-marks. 



Roches moutonnees are characteristic of land-ice, and generally 

 shew a difference between the strike side and the lee side. They are 

 counterfeited by the weathering of homogeneous eruptive rocks — 

 such as granite — especially where a concentric structure has been 

 developed. 



Ice-scratches and grooves on bed rock — formed by land-ice or by 

 iloating-ice. Those formed by floating-ice are rarely straight, and 

 may be much curved. Those formed by land-ice are straight or 

 slightly curved ; they occur on surfaces which may be horizontal, 

 inclined, vertical, or ■ even overhanging ; and also on curved or 

 inamillated surfaces. The counterfeits are slickensides ; rain grooves 

 in calcareous rocks ; and sand drift grooves. 



Ice-scratched stones. These are common in boulder clay, which 

 is supposed to be the ground moraine of an ice-sheet, but are rare in 

 the remains of glaciers. Often the scratched stones are rounded by 

 water-wear, and scratched all over, but sometimes they are facetted 

 on the scratched side. Shore-ice causes irregular shallow scratchings 

 only. They are counterfeited by stones in fault rock, by stones in 

 landslips or even those that have undergone soil cap action only. 

 But these stones are never facetted and the scratchings are usually 

 irregular and shallow. In some cases of basic eruptive rocks, 

 irregular decomposition produces apparent scratches and grooves. 

 Facetting is produced by sand drift, but the facets are generally 

 curved. 



Kettle-holes are small basin shaped depressions in gravel or in 

 morainic matter, caused by the melting of detached blocks of ice 

 which have been covered up by detritus. 



Giant Kettles, or Pot-holes, are cylindrical holes worn out in solid 

 ro3k by the friction of stones under waterfalls or glaciers. 



Moraines are always present in recently glaciated districts ; and 

 are among the most permanent of ice-marks. Nearly all glaciers 

 leave behind them a terminal moraine across the valley ; and in 

 North America a large moraine marks the front of the old ice-sheet. 

 Counterfeits are landslips, but these can generally be distinguished 



