There are headstones that are laid flat on the ground. Almost 'inlaid' into the ground. My best guess is due to a lack of adequate maintenance. The headstones are laid at the foot of each walkway in the open grassy areas. for instance, in this picture...
...the graves are in the grass, two bodies across, with the head stones at each side of the walkway. I'll check my pictures when I get home this evening and see if I don't have a better photo of the headstones.