1. The problem statement, all variables and given/known data The problem is here: 2. Relevant equations q = heat flow k = thermal conductivity q = -k (dT/dY) 3. The attempt at a solution While this is quite an easy question, I just want to verify that I'm doing it correctly. Would it be correct to begin at the bottom of the rock layer, since heat flow will migrate away from the source, which is at depth? So, for bottom layer of sandstone, q = - 5.3[ (274.266 / (465-412) ] = 27.4 Wm-2, where dT comes from converting the change in temperature (in celcius) to Kelvin. Then I move on to the middle shale layer: q = - 1.7 [ (273.609 / (412-402)] = -46.5 W/m2 . However, I am confused how the previous heat flow will affect the heat flow above it. Again, it's an easy question, but I'm hung up on something... Thanks!