History of medical practice in Illinois - Bushnell Historical Society

Medical Geography of Illinois 9geologic changes resulting in elevations and depressions had exchangedpositions repeatedly, depositing and eroding, at times regularly but moreoften irregularly, enormous masses of earth material. It has also beenlearned that in later eras there were other alterations resulting in mountainsand valleys, together with complex topographic changes in the regionswhere the Great Lakes and adjacent rivers now are. Much of the Illinoiscountry at one time was lower than at present.Later lime rock was depositedand at present underlies the Chicago region. But far to the northwere ancient highlands, rich in elements, minerals, ores, soils and rocks.Here lay Laurentia, "the nuclear shield of the North American Continent."The Ice AgeLong after the phenomena mentioned above, there occurred in rhythmicsequence another important global event, namely, the succession of massiveglaciers which advanced in tongue-like segments from the north and thenortheast. The evidence is unmistakable that at least at four different timeslarge regions of the world were denuded by iceand later deluged by thewater, soil and rock resulting from the melting and the movements ofthese glaciers. The Illinois country, in particular, was thus repeatedlywashed down and leveled off by these ice-water masses. The ice not onlydescended from the north and northeast, but at the same time great riversapproached both from the east and west, bearing rich sediments which weredeposited along the way. In this manner a covering of rich soil and debris(till)extended over most of the state. With this fertile soil and with favorablerainfall and climate, in postglacial times the plant and animal lifefound conditions so well adapted for growth and development that few ifany regions on the continent have equalled it in the variety and abundanceof its fauna and flora.Associated with living forms, sooner or later the appearance of diseasesof one kind or another is the invariable rule, in fact is inevitable in allknown biologic systems. Agents of disease—bacteria, viruses, parasites, insects,poisonous plants and animals—and predators in great numbers originatedor developed in this early biologic era in Illinois, all engaged in agrand struggle for existence.The ice, advancing toward the south, covered the entire state with theexception of three small areas: one in the extreme northwest corner in theGalena region, a second in the extreme southern end of the state, and athird just above the junction of the Illinois and Mississippi Rivers. Theseareas are known as the driftless regions and are differentiated by their moreirregular topographic contours, absence of glacier boulders and of recentglacial moraines and their associated phenomena.If one examines a map of the Illinois moraines (Bulletin Illinois State