azvolrien:Hello, it’s time for Rock Facts.What you’re looking at in these photos is call
azvolrien:Hello, it’s time for Rock Facts.What you’re looking at in these photos is called Hutton’s Section, after the 18th-century scientist James Hutton. It’s a smallish stretch of exposed rock at the foot of Salisbury Crags, and as my sister mentioned in her video earlier, it’s actually a pretty important site in the development of the science of geology. About 325mya, a subterranean magma intrusion forced its way through the existing sedimentary rocks; you can clearly see in the photos where the layers of sediment meet the more solid, relatively uniform material of the dolerite, the rock that that long-ago magma sill solidified into, and also where the layers have been variously sheared off or bent out of shape by this, like someone prising up a recalcitrant floorboard. What we can also see is that the sedimentary rock must have been much colder than the magma: looking closely at the border where the rock types meet (fourth picture) reveals what’s called a ‘chilled margin’, where the rock is very fine-grained. This shows that the magma cooled rapidly on meeting the sedimentary rock, effectively forming a volcanic glass now much broken up by erosion over the millions of years since. -- source link
#geology#dolerite#igneous#chilled margin#science#lensbong#hutton#salisbury crags