Most genre representing albums

if they're grind, how can they release the quintiessential death metal album??

and yea you're right about metallica... their 1st 2 albums are speed/thrash

Bands change the genres they play sometimes.

I understand it is a hard concept for you to take, seeing as how all that muscle cuts off half of your brain's oxygen supply and all, but it is true.

Metallica were never speed anything. Speed metal is like early Blind Guardian and Helloween's first album, whose Metallica have never sounded like.
 
isn't carcass pure grind??? every website lists them as a grind band (and offcourse they become melo death later)

is there something I'm missing???

Um... didn't you just answer your own question? Carcass started off as a grind band but went on to different territories quite quickly.

Reek of Putrefaction - Grindcore (and quite a bad album, in my opinion)
Symphonies Of Sickness - Grindcore with death metal influences seeping in
Necroticism - Death metal
Heartwork - Melodic death metal
Swansong - Death n' roll (not really a proper genre but that is what I would classify it as, kind of similar to later Entombed in that it is heavily built on rock and roll groove, but with extreme metal trimmings)

Calling a band that only made one and a half grindcore album a "pure grindcore" band is a bit silly isn't it?
 
Mort, actually Kill 'Em All is VERY MUCH SO Speed Metal, as are Megadeth and Anthrax. These bands overlap between Speed and Thrash, as does Whiplash, and I'm sure there are many more examples of that.
 
I could see Ride The Lightning overlapping Speed Metal slightly, but not so Kill 'Em All, despite the hefty Motorhead influence (and no, I'm not doing the whole "Motorhead are speed metal / Speed metal doesn't exist" argument again)
 
Kill 'Em All is basically NWOBHM after an 8-ball or two. Diamond Head, Motorhead, Holocaust, and Satan in a blender. That is what I call Speed Metal, and this is where Thrash Metal began, but they went in slightly different directions. So basically what I'm saying is that it's acceptable to call Kill 'Em All either term. I definitely call Ride The Lightning Thrash though.