In reply to McHeath:
> And what exactly (maybe we've had this discussion here before) is a "vertical slab"?
The French word "dalle" is used to describe a fairly blank sheet of rock. Indeed the same word is used for sheets of wood. In that sense it isn't far removed from our word "slab", which also describes smooth sheets of building materials.
Both words were adopted as climbing terms a long time ago, and I suppose if the subject is climbing and you're talking about sheets of pretty featureless rock, you're usually going to be looking at pretty low-angled features.
I don't know whether the French had more vision that vertical "dalles" could also be climbable, or whether the rock types made that more feasible, but in any case it seems like where the English term "slab" has become synonymous with low angled rock, the French term "dalle" also includes much steeper walls as long as they appear reasonably featureless from a distance. Although I've yet to hear anyone refer to a radically overhanging but apparently featureless wall, such as some of the faces at Céüse, as a "dalle".
The article's use of the term "vertical slab" is clearly a direct translation from the French. I agree that technically it makes little sense in English, but I think it does a good job in conveying the largely holdless nature of much of the climbing being described.