Na, the cart drives over pressure plates which turn the signal on/off for a piston which is restricting the water flow :)
And yeah - the track has powered bits in. Give it a push and it'll keep going forever :)
I'm pretty sure it's already been discussed, but I don't want to have to reread this entire thread to find it - how many blocks high can you build from 'sea level' (I'm guessing the sea level's constant throughout the map).
Got a little project that's going to be 71 blocks high and I need to know whether I need to dig down to fit it all in!
Also - how easy is black wool or wool and black dye to come across?
Does anyone have any vast stocks of the stuff?