I thought that there was a topic for asking questions without starting a discussion, but I couldn't find it (plus I'm on my laptop on vacation). If a moderator knows of a more proper topic to place these questions in, do please make the necessary corrections.
1. Walking along yet another medieval wall, this time in Porto Venere, I noticed the variety of rocks used to build that wall.
Question: Is or was one first step of a geologist setting out to study the geology of an area to visit such old constructions in order to see what the previous generations had found around there?
2. Physics question. There's a rotating exhaust vent which is very shiny, highly reflective. At night it seems to have a prismatic effect as it takes yellow and white street light light and generates a rainbow of colors -- mainly we see glints of red and blue along with white. Is there an explanation for that effect?