a block is just a header, a ref to the previous block, a set of tx's and a nonce to satisfy the work function.

It being digital is just its encoding. An analog cryptocurrency could be carved into trees or anything.

Are you confusing digital with electronic? Ones and zeros carved into a tree are still a digital record. Digital refers to the fact the you operate on a set of discrete values, in contrast to a continuum of values. Medium is irrelevant.

Just to be clear. I do agree with the argument above that "cryptocurrency" is a much more fitting term than "digital currency".

Yeah, I think I am confusing the two.

I suspect there are chemical compounds that when reacted can perform analog arithmetic. If you used that to create signing, hashing and propagation logic I dare say analog cryptocurrencies could exist.