Tuesday, June 19, 2007

Till, we meet Again!

Whidbey Island has many Till layers, from the Ice Ages, at least 14,000 years ago. Till is an unsorted glacial deposit, which was dumped under the ice or left as uneroded sediments after the ice was completely melted. It has never been subjected to stream working, and rock roundness is due to the individual cobbles having been transported by water before they were dumped onto the ice.

Notice that there are many sizes of rocks, generally grey in appearance- due to coating with rock dust. They make poor soil, since they have little organic material entrained; weeds hardly grow in this type of surface. The easiest feature for identification is that of lack of stratification- water never having sorted the mix.