Please note that when mining the floor you can create uneven surfaces thus making it hard to move around in your mine. For the best access in a mine it is recommended not to mine the floor directly unless you have a plan for it. The actions "mine up" and "mine down" create somewhat predictable slopes of 20 and are good if you want a sloped passage, although floor mining can be very useful if used in the right way. Proceed floor excavations with caution as the mining is not easily reversed. When digging you can always drop the dirt and refill the hole - this is '''not''' possible when mining.
You can fix slopes with --Concrete-- one concrete will raise one corner, the equivalent of 1 dirt, (or 1 mine action)
It's advised that you mine cave ceilings when in need of rock shards it's faster than mining the caves walls.