The gneiss appears nearly impervious to erosion compared to the other materials. This differential hardness allows rapid erosion and mass wasting of the weather gneiss and clay while little change occurs in the vergin gneiss itself. The streams in this area easily erode the land until the base of the pre-existing weather zone is reached causing streams to reveal a image of the ancient land surface only a few feet lower. Why does the unweathered gneiss appear unaffected today when it obviously succumbed to weathering in the past?

In modern Minnesota's climate conditiions are great for rapid physical weathering during spring and fall freeze thaw cycdles but are not favorable for chemical weathering that increases exponentially with increases in temperature. More than a billion years ago Minnesota was in a moist tropical environment, much like Brazil is today. The lateritic soils dominated by light colored clays and quartz sands typical of Brazil bear stong resemblance to the soil here. Sansome, 1983 reports, weathing of felsic igneous rocks in Hong Kong chemically and structurally similar to the Morton gneiss show soil profiles and compostion very similar to the soil here. The soil here gives evidence that Minnesota must have existed in a similar moist tropical landscape for at least a million years (Sloan 1964).