“Okay class, as you can see from the formation to my left and right, there are prominent dark lines moving vertically through this siltstone. According to the law of original horizontallity, layers of rock should be horizontal to begin with. Now, if you look closer, the dark units are composed not of pieces of sediment, but of interlocking crystals. This suggests that these are vertical igneous intrusions, known as dykes. From both these rocks, we can assume that the siltstone formed in water in particular high energy, as the sorting of the grains is quite uniform. Later, we can assume that the formation of a magma chamber below allowed magma to melt through the siltstone, and eventually cooled in the formation you see now.”
 
“Any Questions?”