@Setanta,
I haven't studied it per se, but I remember a time when I was younger (10 or 11 I think) when I was interested in rocks and I probably read a few of those geology field guides. Sometimes I remember images from the book and the words below the image.
In this particular case I doubt I have it right because no strong image came to mind, but those were the words that popped in, so I went with it