I had the same problem in 34.02, gabro, granite, marble, and some others all the way to the bottom, with the only metals being some native gold, platinum, and cobaltite, even when I had volcanism set to its absolute minimums and mineral scarcity at maximum. I hadn't played since 40d so this was a bit strange to me, but it seems sedimentary layers are MUCH rarer in good locations (ie next to mountains you can dig into) than they used to be. Rare as they are they do exist however, and the best way I've found for getting to them is to go into your raws and delete the flux tag for marble until you find your embark location. To do this go into your DF directory > Raw > Objects > inorganic_stone_layer.txt, and look for the entry for marble (mine is at the very bottom) and delete the bit that says [REACTION_CLASS:FLUX]. This will keep the embark finder from seeing marble as a viable flux and returning the entire map as a good embark location, and will point you to places that have flux that are much more likely to have useful metals in them (usually limestone). Keeping the tag off will make it so marble won't function as a flux stone however, but you can add it back in after you find your desired embark location. It will still take you some effort to find a good embark location still, but I was able to find a solid one this way with a huge cliff faced mountain (going up about 40 z levels straight up above the river level) that's almost all sedimentary with lots of metal and limestone above the surface, and much more sedimentary goodness around the river and down about 7 z levels beneath it (The rest is the usual rock that I had been getting). I also second Flying Dices notion of using dfhack to help your search, as it made it a hell of a lot less tedious and annoying for me. Using prospect on the embark screen will give you a general view of whats in the embark location if thats all you want to know, or if you're a construction and megaproject person like me you can go in and reveal the map to see exactly what it has and if you'll be able to pull off what you're going for.