The old gunpowder mills

I took one of the kids for a cycle down to where the old old gunpowder mills used to be. We stopped beside this

Am I right in thinking that this would have been used for making the charcoal for the gunpowder or was there some other purpose for it?

I think (I'll need to check) that was the base of a chimney stack.

I've not seen that before, where is it?

Go to Roslin and turn off down the road to Rosewell. (There are signs up saying the road is closed, but you are still allowed access to up to a certain point along it.) At the bottom of the hill, there's a hair-pin bend with gates on the right hand side. The old powder mill is through those gates.

If you can't park outside the gates, drive on just past the sewage works and you'll find plenty of parking in the Roslin Glen Park.

A dirt road leads right through the old mill and there are still a few remnants of the old buildings. About 25 years ago, however, there were many more and the place was like an old deserted village.

I  haven't been round the old Gun Powder factory for some time, but revisited it again today.

One end of the weir has gone. Does anyone know whether this was due to "natural causes" or a demolition crew? Believe me, or believe me not, but some years ago, on two successive Septembers, I saw either salmon or sea trout trying to get up that weir. Life might be easier for them now, if they ever return.

I can't remember if I've asked about this before, but I'll ask again anyway. As you walk back from the weir towards Roslin, there's a rock with 1815 carved into it, about 12 ft above you on the left. I'm guessing it's there to commemorate The Battle of Waterloo.

A few yards further along, also on your left, there's a rock no more that about a foot high, with the date 1859 carved on it above the initials J.H. and J.M. (It might be J.M. and J.M. - there's slight damage to one of the letters.)

Does anyone know what (or who) that might commemorate? The Crimean War had ended a few years before 1859 and the only significant wars going on around that time were in Italy and also between the French and the Prussians. So I'm wondering if it relates to something else entirely. An accident perhaps? But does anyone know for sure?