I think I've got one world where I did a fair bit of deep mining and got a decent amount of iron (even after building armour and buckets and stuff) - when I found out that depth actually made a difference, so I actually dug down deep - but I wasn't fond of the location of that one, so I gave up on it.
Other than that I've been mainly building/sculpting basic things, and not yet got around to doing more mines below sea-level to actually get the rarer ores.
Hah. Work network is frequently slower and laggier than 3G. :/
Not to mention there isn't a private place I could go to do it, and doing it in public I'd get shouted at for clogging the network at any time, since lunchtime can be any hour between midday and 3pm for different people.
Sounds like you jumped into an unloaded chunk. My canal is flat and level. Any perfectly edged holes straight down to bedrock are a server bug. Logging out then back in normally persuades the server to load that chunk.
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