From The Two
Towers,
The Choices of Master Samwise:
'They would,' grunted Gorbag. 'We'll see. But anyway, if it does go well, there would be a lot more room. what d'you say?--if we get a chance, you an me'll slip off and set up somewhere on our own with a few trusty lads, somewhere where there's good loot nice and handy, and no big bosses.'
'Ah!' said Shagrat. 'Like old times.'
Here's one quote that always gave me the impression that
orcs had long life spans. Shagrat certainly seems to be reminiscing about something he lived through, and from what I know of
Middle-Earth history there wasn't any prolonged period of time in
the third age that an
orc would have thought of as good ol' times. That sounds like something more out of the
second age, when the initial expansion of
Mordor went largely unchecked.
The seige quote (By Gorbag):
'You may well put your thinking cap on, if you've got one. it's no laughing matter. No one,
no one has ever stuck a pin in
Shelob before, as you should know well enough. There's no grief in that; but think--there's someone loose hereabouts as is more dangerous than any other damned rebel that ever walked since the bad old times, since the great Siege. Something
has slipped.'
I'd say that he's definitely talking about the siege of
Barad-dur here. In all of
Tolkien's works I don't know of any other great Siege in Mordor. Of course, in this case Gorbag doesn't quite use the language that would definitively place him at the siege. Oh well. What I reall do like about this chapter is that it gives us a good look at Orc culture- what their motivations might be, etc. I certainly think that they are different from 'the beasts'. Gorbag is at least able to put some thoughts together fairly quickly and figure out a lot more about what is going on in the wide world than his superiors might want for him to know.
Anyway, I think that the orc mortality question goes with a lot of the discussions regarding how Tolkien was always going back and re-writing his works. Orcs were originaly intended to be corruptions of
Elves, and so probably would have had some characteristics in common. However, as time wore on (after the publication of LotR, I believe) Tolkien began to feel that Orcs were more akin to corrupted
men. One of his comments in HoME certainly seems to indicate that he was considering the Orcs as corruptions of men, which could have meant that he would then go and revise the passage of
the Silmarillion so that this idea would be consistent. Unfortunately the good professor never got the opportunity to go back and do this, so we have Orcs descended from Elves and Gorbag reminiscing about what appears to be the second age.