Middle School Science: Rock cycle in Door County, Wisconsin

When you walk on the beach, do you ever stop to wonder where the sand came from? Why are some beaches gravel instead of sand, and yet others are just limestone bluffs dropping straight down into the water?

These pictures were taken on a beach in Northern Door County. Apparently dolomitic limestone beaches are a fairly rare phenomenon; this is one of them. The parent bedrock is a hardened cap of dolomitic limestone from the Niagara Escarpment over a slate base. Perhaps you haven’t heard of this escarpment before, but you already know a fairly famous waterfall that flows over it! So if this escarpment is so hard, how did Lake Michigan form? The Ordovacian and Devonian layers surrounding this relatively thin wedge of limestone are softer and have eroded away over the years, forming depressions that eventually formed many lakes as the glaciers receded, Lake Michigan among them. The Niagaran Escarpment is Silurian and was more resistant to the glacial carving. Even so, it flakes apart very easily!

One can almost see the rock cycle taking place from year to year, as this author has noticed automobile-sized boulders flake off from time to time. The wind, water ice and waves all do their part in nature’s rock tumbler to make a beach with rock sizes varying from pea-sized to walnut size. But if the parent bedrock is only limestone and shale, how is it that the beach is covered with samples of basalt, agate, chert, and many other specimens? Glaciers are the culprit! How about the three types of coral – honeycomb, chain and tube – how did they get into a fresh water lake, along with a plethora of other fossils? Come by the lab and inquire within if you aren’t sure! 🙂

– Mr. S

 

 

Rock cycle at work: on the Niagaran Escarpment

Rock cycle at work: on the Niagaran Escarpment

Fossilized coral

Fossilized coral

Screen shot 2016-01-11 at 1.39.54 AM

Screen shot 2016-01-11 at 1.37.37 AM