Opus 40 – More Geological Finds


Opus 40 – Little Balls of Mud.

We have been exploring the quarry at Opus 40, near Woodstock in recent months. This is just the sort of thing that geologists do all the time. We visit a new location and just poke around, seeing what we can see. You can’t do this without finding all sorts of interesting things and we have been describing many of these during the past two months. But we always find problems as well. And indeed, that was the case at Opus. Take a look at our first photo. It shows some things that troubled us. Do you know what a conglomerate is? That’s a sedimentary rock that is largely composed of pebbles and cobbles. Often, they are rounded from having been rolled around in the river currents. And that is exactly what our photo seems to show.

But, what, we asked, were cobbles doing in a river channel deposit? Where had they come from? How did they get there? River channels like these should be filled with sand and little else. You can see that this was, indeed, a problem. We couldn’t figure this out so we just went on exploring. And then it happened, in a flash, something scientists commonly call the “ah hah” moment. Take a look at our second photo. There you will see more of our cobbles. But the knife joins two which show a lot more. Suddenly we had our ah hah moment. Take a look; can you figure it out? We will give you ten seconds . . . 10, 9, 8, 7, 6, 5, 4, 3, 2, 1 and ???.

Well, this is what we think we are looking at. These two rounded cobbles had been broken open, exposing cores. The cores of those two “cobbles” are bits of petrified mud. They likely eroded out of a muddy upstream river bank way back during the Devonian. Sometimes geologists call such things mud blebs. Those mud blebs were caught up in the river currents and rolled around until they had become rounded. Then they encountered a sandy stretch of the old river and then a coating of sand adhered to the sticky muds. You can see that on our photo. And, presto, there we had our “cobbles” and there we had our explanations.

This is not great science. The discovery of the polio vaccine? That was great science. The discovery of mud blebs? Not so great. But, like all science, this was a lot of fun!

Contact the authors at randjtitus@prodigy.net. Join their Facebook page “The Catskill Geologist.” Read their blogs at “thecatskillgeologist.com.”