Résumé

In order to illustrate how glacial stratigraphy may become influenced by the subjectivity of researchers, the grain size composition of till will be discussed as an example. Most particle size data do not refer to the entire till, but mainly to its matrix, plus smaller clasts. Though the granulometric data, even if just referring to till matrix, are considered to be reliable and objective, various amounts of subjectivity enter the analytic results during the sampling, pretreatment, analyses and statistical evaluation of data. The subsequent interpretation involves even more subjectivity. This will be illustrated by using tills of Southwestern Ontario and Denmark as examples. While colour and texture of till once used to be the main criteria for differentiation and correlation of tills, more complex multiple criteria are applied now. During the last 15 years a score of genetic varieties of tills have become recognized, each of them playing its role in stratigraphic interpretation. Now more attention than before is paid to glaciotectonic deformations and fabric in deciphering stratigraphy of glaciogenic sequences. Quaternary glacial deposits cover most of Canada. If their stratigraphy has been properly deciphered, the extraction of Quaternary economic deposits and the planning of major construction projects may be done rationally. The knowledge of glacial stratigraphy is useful also in hydrogeology and in planning waste disposal. In the search for bedrock ore deposits by indicator tracing, an understanding of Quaternary glacial stratigraphy is essential in areas with more than one layer of glaciogenic deposits over bedrock.