222 



GIZEH 



GLACIAL PERIOD 



Gizeh, or GHIZEH, a small town in Egypt, on 

 the opposite side of the river from Old Cairo, and 

 approached from Cairo by the great swinging bridge 

 constructed over the Nile in 1872. It was formerly 

 fortified by the Mamelukes, but is now a poor place, 

 though it has some cafes, dilapidated bazaars, and 

 a pop. of 10,500. Artificial egg-hatching has been 

 practised here since the days of the Pharaohs. The 

 pyramids of Gizeh are not close to the town, but lie 

 five miles away to the west. See PYRAMID. 



Gizzard. See BIRD. 



Glacial Period, or ICE AGE, is a term used 

 in geology to designate that period the records of 

 which are included in the Pleistocene System (q.v.). 

 ' Glacial period ' and ' Pleistocene period ' are in 

 fact synonymous as regards all northern and tem- 

 perate regions the former term being used when 

 the prominent climatic characteristics of the period 

 are thought of, while the latter is employed with 

 reference to its life. The chief geographical and 

 climatic changes of this period, and the general 

 features of its fauna and flora, will be considered 

 under PLEISTOCENE SYSTEM. But here a short 

 account may be given of the relics which furnish 

 evidence of former glacial conditions having obtained 

 in many regions that are now in the enjoyment of 

 temperate climates. It is chiefly in the northern 

 parts of Europe and North America, and the hilly 

 and mountainous districts of more southern lati- 

 tudes, that the glacial deposits, properly so called, 

 are developed. These deposits consist partly of 

 morainic materials, erratics, &c., and partly of 

 marine, fresh-water, and terrestrial accumulations. 

 The most important member of the series is Boulder- 

 clay (q.v.), or, as it is often termed, till. This is 

 an unstratified clay, full of ice-worn stones and 

 boulders, which is believed to have been formed 

 and accumulated under glacier-ice. Several dis- 

 tinct and separate sheets of boulder-clay have been 

 recognised, divided from each other by intercalated 

 ' interglacial beds,' which last are often fossilifer- 

 ous. The lowest and oldest boulder-clay covers 

 vast areas in the British Islands and northern 

 Europe extending south as far as the Bristol 

 Channel and the valley of the Thames in Eng- 

 land, and to the foot of the Harz Mountains, &c., 

 in middle Germany. Boulder-clay of the same 

 age spreads over the low grounds of Switzerland, 

 and extends from the great Alpine valleys for many 

 miles into the circumjacent low-lying regions. 

 Similar ground-moraines have been met with in 

 all the mountainous and hilly tracts of Europe, 

 as in central France, the Pyrenees, the Spanish 

 Sierras, the mountains of Corsica, the Apennines, 

 the Vosges, the Black Forest, the Erzgebirge and 

 other ranges of Germany, the Carpathians, &c. 

 The rock-surfaces on which the boulder-clay rests 

 are often smoothed and striated, or much crushed 

 and broken, while the hills and mountain-slopes 

 in regions where boulder-clay occurs give evidence 

 of having been abraded and smoothed by glacial 

 action (see ROCHES MOUTONNEES). At the time 

 the boulder-clay was formed, Scotland, Ireland, the 

 major portion of England, Scandinavia, Denmark, 

 Holland, the larger half of Belgium, Germany as far 

 south as Leipzig, and vast regions in Poland and 

 Russia were covered with a great mer de glace. Con- 

 temporaneously with this ice-sheet all the moun- 

 tain-regions of the central and southern regions of 

 the Continent nourished extensive snowfields and 

 glaciers, which last flowed out upon the low ground 

 often for very great distances. Thus, Lyons stands 

 upon old moraines which have been carried down 

 from the mountains of Dauphine and Savoy. The 

 interglacial deposits point to great changes of 

 climate when the snowfields and glaciers melted 

 away, and temperate conditions of climate super- 



vened, as is shown by the geographical distribution 

 of these deposits, and by the character of the plant 

 and animal remains which they have yielded. The 

 youngest boulder-clay, overlying, as it does, such 

 interglacial beds, proves that the glacial period 

 closed with another advance and final retreat of 

 the Scandinavian ice-sheet and the great glaciers 

 of the Alps, &c. The terminal morsfines of the 

 last ice-sheet do not come so far south as those of 

 the first and greatest mer de glace. These moraines 

 show that the ice covered the Scandinavian penin- 

 sula, filled up the Baltic, invaded north Germany, 

 and overflowed Finland and wide regions in the 

 north of Russia. Similarly in the Alps, &c., the last 

 great extension of the glaciers was not equal to that 

 of the first. See EUROPE. 



The boulder-clays are not the only evidence of 

 glacial conditions. Besides those accumulations and 

 the scratched and crushed rock-surfaces already 

 referred to, we encounter numerous erratics (see 

 BOULDERS, Erratic), eskers or kames (see ASAR), 

 Giants' Kettles (q.v.), clays with Arctic marine 

 shells and erratics (in Scotland, Prussia, &c.) the 

 organic remains associated with the glacial deposits 

 often affording strong evidence of cold conditions. 

 The following table shows the general succession of 

 the glacial deposits in several parts of Europe : 



SCOTLAND 

 6. Valley-moraines and fluvio-glacial gravels = small local 



glaciers. 

 6. Kames, erratics, fluvio-glacial deposits, laid down during 



retreat of last general ice-covering. 

 4. Clays, &e., with Arctic marine shells, occurring up to a 



height of 100 feet deposits belonging to the period of 



retreat of mer de glace, and contemporaneous to a large 



extent with those of 5. 

 8. Upper boulder-clay := moraine profonde of latest mer de 



glace. 



2. Interglacial beds == disappearance of cold conditions ; 



clothing and peopling of the land-surface with temperate 

 fauna and flora ; subsequent submergence to not less than 

 500 or 600 feet below present level. 



1. Lower boulder-clay with intercalated interglacial fossil- 



iferous beds = the product of more than one mer de glace. 



The lowest clay marks the period of greatest glaciation. 

 ENGLAND AND IRELAND 

 6. Valley-moraines and fluvio-glacial gravels. 

 5 and 4. Kames or eskers, erratics ; fluvio-glacial deposits. 



3. Upper boulder-clay of last mer de glace. 



2. Interglacial beds, marine and fresh-water. Disappearance 



of glacial conditions ; land-surface at first ; subsequent 

 submergence to considerable extent. 



1. Lower boulder-clays with intercalated aqueous deposits, 



indicating probably same conditions as 1 in Scottish 

 series. 

 NORTHERN EUROPE 



4. Sand and gravel; erratics; shelly marine clays (in Baltic 



area ). 



3. Upper boulder-clay and terminal moraines of last mer de 



glace-. 



2. Interglacial beds, partly fresh-water and terrestrial, partly 



marine. 



1. Lower boulder-clay = greatest extension of ice. 

 SWITZERLAND 



4. Fluvio-glacial gravels in terraces. 



8. Moraines and upper boulder-clay of last great glaciers. 



2. Interglacial beds, with mammalian remains, &c. 



1. Lower boulder-clay. 

 CENTRAL FRANCE 



4. Fluvio-glacial gravels. 



3. Moraines. 



2. Interglacial beds, richly fossiliferous. 

 1. Ground-moraines ( Mont Dore ). 



In North America glacial deposits are developed 

 upon a great scale, and there, as in Europe, the 

 boulder-clays are separated by interglacial deposits. 

 The northern part of the continent was drowned in 

 ice during the greatest extension of the mer de 

 glace, the ice flowing south into New Jersey, 

 whence its front extended north-west through 

 Pennsylvania, after which it trended south-west 

 through Ohio and Indiana to reach the 38th parallel 

 of latitude in Illinois. It then appears to have 

 swept away to the north-west in the direction of 

 the Missouri valley. The latest American mer de 

 glace did not come so far south its terminal 

 moraines being well developed in Minnesota, Wis- 



