I g Communications cat t t e Jr J ff THE GLACIAL EPOCH The forces of nature lature are always active in modifying the physical aspect of the t surface of the earth Mountains are disintegrated disintegrated dis dis- integrated by chemical forces and the fine materials are carried by mechanical agencies agencies agencies agen agen- cies into the hollows and plains and there deposited The general tendency of these forces combined is to lessen the inequalities inequalities in in- inequalities equalities of the earths earth's surface by wearing wearing wearing wear wear- ing down do the elevations and filling up the depressions We have the Alps and the polar r regions re regions re- re gions at the present time vast masses of moving ice called glaciers which act as as powerful agents of er sion and tation These masses moving slowly down the slopes and gorges of the mountains mountains mountains mountains' moun moun- gather in their course l large rge quantities ties of m material from the adjacent cliffs and the beds over w which h ch- ch they move In high latitudes the glaciers generally reach the sea where they are broken into smaller masses by the buoyancy of the water and the beating of the waves called iceK icebergs icebergs ice K These floating masses are bergs Many of these are carried by ocean currents to lower latitudes where they are melted and their burdens are deposited on the bottom of the sea The banks of Newfoundland are now being built up from such deposits In the temperate regions the glaciers do donot donot donot not reach the sea but they teI terminate minate in inthe inthe inthe the v valleys ll ys where the temperature is sufficiently sufficiently suf suf- high to o keep them from advancing advancing advancing ing further The debris is here deposited and in the course of time large moraines t. t hj are formed These land deposits are characterized characterized char char- by the presence of angular and andr r scored of all sizes and by the absence o of stratification and fossils The study of these agencies and formations formations formations form form- are not only interesting and instructive instructive instructive tive to persons concerned with the history of the present epoch but the study is of special value to those interested in the past history of the earth Since the agencies agencies agencies agen agen- cies now operating ng are the same as those t that have always acted in modifying the ther r earths earth's surface though they may have acted with greater greater- intensity ity in former r times times we get the key to the past history by studying what takes place before us at atthe atthe t Y the present time By the study of these II Jb t mo modern d ern agencies geologists have gained gamed J s' s much valuable information i relating elating to that great epoch of the earths earth's history ft u called The Glacial t Epoch Over large areas of the eastern and the thet t y I northern part pait of the United States and andI andover over the greater portion of Canada extends extends ex ex- r- r ten tends s on hill and valley a peculiar earthy L deposit varying in thickness from a few inches to four and five hundred feet feet No formation like it has yet been bee found in tropical or tropical sub-tropical regions It consists consists consists con con- of clay sand gravel angular and semi-angular semi weighing sometimes sometimes sometimes some some- Y times many tons tons all mixed together b with rr no sign of stratification so characteristic in 1 water deposits The surface is general generally y covered by a layer of soil deposited by water In many places both on the valleys valleys val val- leys and high upon the hillsides are found large entirely different from the country rock and must therefore have been transported from distant localities Many rocks beneath the surface are aie distinctly distinctly distinctly dis dis- scored d or marked by parallel ridges and depressions similar to the markings found on the rocks of modern glacial deposit The underlying country rock bears unmistakable evidence of glacial glacial gla gla- cial action In some places it is polished smooth and in other places it is scored with parallel furrows many inches deep and again in other places where the rock is softer it is scooped out and the depressions depressions depressions de de- thus formed are marked in many places by fresh water lakes The scorings scorings scorings ings on the bed do not only prove by what agent they were produced but they they- also show from rom what direction the agent came The principal centre of glacial action in North America is proved to have been b between tween the great lakes and Hudson bay From this centre large sheets of ice extended extended extended ex ex- tended in a southeasterly southerly and southwesterly direction into the United States ta es and in a general iener northerly direction over British America In Europe t the e principal centre was in the Scandinavian peninsula from which rivers of ice extended extended ex ex- tended as far south as the Alps and the Pyrenees Geologists have advanced many theories theories theories theo theo- ries to account t for the accumulation of the vast masses of ice duri during g that epoch but but only the two principal o ones es will be considered considered con con- on 1 na namely ely the subsidence subsidence and the i elevation theory j 1 According to the the subsidence theory the a nor northern hern portions of both continents SU subsided subsided sub sub- sided below below the lev level l of of the sea great ina in- in a land seas were formed and icebergs loaded with debris floated from the northern regions regions re- re gions ions o-ions southward and before i reaching caching the theton ton torrid id zone were melted and deposited their loads on n the the bottom of the sea While this theory accounts for some observed observed observed ob ob- served facts it does not account for the most important The chief arg arguments raised against this thi this theory theory is the he regularity of the scoring of the underlying strata over large areas and the absence of fossils in the deposits Such regularity of scoring scoring scoring ing could not possibly have been done by bythe the chafing and rubbing of icebergs on the bottoms where the water was of dent depth to float them Besides that subsidence would have increased the mean annual temperature and arid rendered co conditions conditions condi condi- i- i unfavorable for the accumulation of ice The absence of fossils in the deposits deposits deposits de de- posits is strong evidence against this the the- ory It is known that life was abundant in the seas of that epoch from the fact that fossils are numerous in the deposits formed in other localities during this same period of time According to the elevation theory a general elevation of several thousand feet took place very slowly in the northern part of both continents In America the greatest elevation took place in British America north of the great lakes The elevation lowered the temperature several degrees which favored the accumulation of ice When the ice mass mas became sufficiently sufficiently dently great it moved very slowly from this centre northward to perhaps to-perhaps the Arctic Arctic Arctic Arc Arc- tic ocean and southward as far as southern Illinois where the temperature was high enough to prevent its f further advance When the terminus terminus' became stationary the materials carried from higher latitudes began began began be be- gan to te be deposited and moraines were formed Gradually through long ages compared with which mans man's recorded history history history his his- tory of its existence dwindles into the centre of glacial action subsided subsided subsided sub sub- sided the temperature increased and as the ice sheets receded the deposits took place further and further north thus covering covering covering cov cov- ering in succession large areas of coun country try which in the United States includes the 1 Eastern States and the Northern States as asfar asfar far west as Montana Many fany geologists believe that elevation was not the only cause though they believe believe believe be be- I lieve it the principal one in lowering the temperature astronomical 1 factors are taken into consideration They hold that the eccentricity of the earths earth's orbit was much greater during the glacial epoch than it is at present The difference between between between be be- tween the earths earth's aphelion and perihelion distance from the sun sun would therefore have been much greater than at the present present pres- pres ent time This would in the northern hemisphere make the winters longer and colder and the summers shorter shelter and hotter Owing to the procession pi of the eq equinoxes aphelion winter and perihelion summer comes at regular intervals of about twenty twenty- one thousand years At the present time we have perihelion winter i. i e. e we have winter when the sun is nearest the earth eaith Geikie and other geologists advance the theory that aphelion winter coincident with a period of greatest eccentricity would lower the mean annual temperature several degrees in the northern hemi hemi- sphere Such coincidence they claim took ook place during the glacial epoch at the same time that the elevation of the northern lands took place i iTo To be Continued next week