REGIONAL AND LOCAL DYNAMICS OF PRE-ILLINOIAN GLACIERS IN KANSAS

Striations on bedrock indicate direction of ice flow, but may record effects of localized lobate spreading or divergence around topographic obstructions rather than regional ice movemen. Backtracking of erratics to source outcrops can be reliable if lithologies are unusual. Clasts of pink Sioux Quartzite are numerous throughout a broad fan extending south and southeast from outcrops across southern Minnesota. This indicates considerable spread in flow direction. In contrast, fragments of catlinite (pipestone), are very scarce - except for hundreds of pebbles over a few acres south of Wamego, KS at the extreme southwestern limit of glaciation. This occurrence suggests that a discrete mass of ice containing this unique debris load maintained its integrity from catlinite outcrop to terminal zone, a north-to south distance of 350 miles. Similarly, so-called Lake Superior agates derived from Keweenawan volcanics along Lake Superior are extremely rare in pre-Illinoian till - except for dozens concentrated in a few square miles on the western edge of Topeka, KS. Here movement of ice 650 miles directly from outcrop to point of deposition is strongly indicated. The hypothesized direct flow of catlinite-bearing ice is situated parallel to and 40-50 miles east of the glacial terminus through northern Kansas and eastern Nebraska, suggesting that there was no increment of flow toward the free, melting ice front. Elevations of high, ice-front erratics along the terminal line from Wamego to Kansas City show considerable variation, indicating that the ice surface was ridged, probably along flow lines.