86 



NATURAL SCIENCE NEWS. 



were left, when it receded, filled 

 with slowly melting ice over which 

 the currents from the melting 

 glacier flowed in torrents, deposit- 

 ing clay and sand more or less 

 perfectly stratified and dotting 

 these strata of finer materials with 

 bowlders dropped from icebergs. 



An arctic flora crowded close 

 upon the receding ice front, and 

 following this came the plants and 

 animals of the temperate zone. 

 Centuries, thousands of years, 

 went by, arctic cold again return- 

 ed, and again the glacier pressed 

 southward. In many places it 

 inpinged its first deposit, produc- 

 ing what is called Contorted Drift, 

 in others it tore up the debris left 

 on its former visit, and ground out 

 the autograph first graven on the 

 rocks. In still other places it 

 spared the former deposits, no 

 doubt finding the till frozen hard 

 as adamant, more difficult to 

 erode than the native rock had 

 been. Often where the unyield- 

 ing till held bowlders imbedded in 

 its surface the returning ice instead 

 of removing them would truncate 

 and plane down their upper sur- 

 face, leaving them marked with 

 fresh furrows, grooves and striae. 



The vegetation was again over- 

 whelmed, but not altogether re- 

 moved from sheltered valleys it 

 was left buried beneath glacial de- 

 bris. The buried remains of these 

 interglacial marshes and forests 

 are now found compressed be- 

 tween layers of impenetrable clay, 

 and reduced to about the appear- 

 ance of peat bogs. The nature of 

 these deposits is unmistakable and 

 they are called "swamps" by well 

 diggers. 



In one place in Boone county a 

 swamp 12 feet in thickness was 

 found and beneath a glacial de- 

 posit 46 feet thick. In another 

 place in the same county the 

 swamp was reached at a depth of 

 60 feet, and a third excavation re- 

 vealed a cedar tree buried 100 feet 

 deep. Black muck, filled with 

 leaves, twigs and branches of trees 

 has been found at varying depths 

 over a large part of the state. 



Vegetable, and. sometimes ani- 

 mal remains buried in such large 

 quantities in impenetrable clay 

 could not fail to produce gas, just 

 as submerged vegetation produces 

 gas in surface marshes. The im- 

 prisoned . gas escaping when the 

 clay is pierced, is naturally of lim- 

 ited quantity, and the flow is of 

 short duration, yet it has often 

 been sufficient to awaken wild 

 hopes that it might be an indica- 



tion of inexhaustable quantities be- 

 neath. 



The lake basins, scooped out by 

 the glacier on it former visit, and 

 left filled with ice and sand on its 

 retreat, were again traversed by 

 the ice field and buried deep with 

 the till, so that when left again 

 they were lenticular beds of wet 

 sand enveloped in dense clay. 

 These are the underground lakes 

 and pockets of water found in many 

 localities, and the source of many 

 of our mineral and artesian springs. 



The water from such artesian 

 wells or springs are often charged 

 with organic matter from the de- 

 cay of interglacial forests, and 

 with hydrous peroxide of iron from 

 the bog iron formed in these de- 

 posits. The decomposing vege- 

 table matter sets free organic acids 

 which act on the salts of iron oc- 

 curring in the drift clay with which 

 it is surrounded, thereby render- 

 ing them soluble. This iron held 

 in solution as a ferrous carbonate 

 oxidizes when exposed to the air 

 and is thrown down as hydrated 

 peroxide, a compound which gives 

 "local color" to the neighborhood 

 of mineral springs in the drift re- 

 gion. 



As the glacier slowly and irreg- 

 ularly retreated the water from the 

 melting ice took a prominent part 

 in the configuration of the surface 

 of the country. Sands and grav- 

 els are known to have a strange 

 tendency to shape themselves in 

 mounds and winding ridges under 

 the influence of currents, and while 

 the surface was still partly covered 

 by an irregular sheet of ice con- 

 flicting currents, breaking through 

 gaps in its front and forcing their 

 way towards the channel of drain- 

 age swept away, drifted and whirl- 

 ed the loose detritus into the forms 

 which are the most unmistakable 

 indications of the former existence 

 of glaciers and glacial streams. 

 Among these are the eskers, long, 

 narrow, sharp ridges of gravel and 

 sand, mingled with bowlders of Ni- 

 agara limestone thrown up in lines 

 parallel with the lines of ice move- 

 ment or drainage. 



More noticeable still are the 

 kames, the rounded hills or elon- 

 gated ridges terminating in hemis- 

 pherical mounds, or having a 

 .mound in the middle and sloping 

 symmetrically to the ends. These 

 mounds and ridges, formed by 

 some imperfectly understood con- 

 flict of currents, and so well known 

 as the mementoes of the retreating 

 glacier, are sometimes mistaken 

 by ill informed people for the arti- 



ficial mounds and fortifications of 

 the "mound builders." 



When in its final retreat the gla- 

 cier reached the northern part of 

 the state the Wabash Arch again j| 

 become powerful in modifying its 

 action, turning aside the glacial tor- 

 rents and restraining the floods 

 with their attendant debris and 

 bowlder laden icebergs from 

 sweeping with their force over the, 

 south, thus increasing the depth 

 of the accumulations in the north. 



At length as the great Ice Age 

 neared its close and the glacier re- 

 treated, into Canada the surface of 

 the state began to assume its mod- 

 ern aspect. Still for a long time 

 Lake Erie poured its waters, by 

 way of the Maumee, through the 

 Wabash, and the Wabash, winding 

 along the northern side of the mo- 

 rainic dam and finally forcing its 

 passage to the south-west, flowed 

 over a wide expanse of country, 

 leaving evidences of its eroding 

 and sorting power on the sides of 

 hills miles from its present chan- 

 nel. 



When at length their northern 

 outlets were freed the waters of 

 the lakes receded and the Wabash 

 shrank to its present proportions. 

 Lake Michigan withdrew from its 

 old shore lines, leaving wave wash- 

 ed terraces to show where it had 

 been, and laying bare the broad 

 "sand barrens" which cover the 

 north-western corner of the state. 



In northern Indiana beautful lit-' 

 tie lakes are still numerous in the 

 hollows scooped out by the ice, but 

 the extensive system of shallow 

 lakes which once dotted other 

 parts of the state were drained by 

 natural agencies, and left in their 

 places "prairies" showing lacus- 

 trine deposits, but destitute of 

 shells, except diatoms. 



For thousands of years the ele-J 

 ments have labored to efface all 

 traces of the ice age, but in vain. 

 Evidences of its work are to be 

 seen on every hand. Every exca- 

 vation and railroad cutting reveals 

 its sign manual on the grooved 

 and striated rocks. The high 

 ground everywhere is cut through 

 by the wide, deep channels of gla- 

 cial torrents now traversed by lit- 

 tle streams wholly inadequate to 

 erode the gorges in which they 

 flow. 



The moraines, in spite of time, 

 are still lofty ridges crowned with 

 "dykes" of granite bowlders. 

 Bowlders of granite, gneiss and 

 greenstone strew the ground, and 

 in many places become serious ob- 

 stacles to cultivation, though this 

 evil is often turned to good account 



