Which of the following are block mountains?

Mountains are classified by how they were formed. Fold mountains arise when tectonic plates collide and compress rock layers into folds along convergent boundaries; block mountains (horsts) arise when a large crustal block is uplifted or tilted between parallel faults, while the down-dropped block beside it sinks to form a rift valley (graben).

Applying this distinction: the Vosges range in eastern France was raised as an uplifted crustal block along faults bordering the Rhine Graben, with the sunken block beside it forming the Rhine rift valley -- the textbook process that defines a block mountain.

• Himalayas: raised by the head-on collision of the Indian and Eurasian plates, which folded and thrust sedimentary layers upward -- a fold-mountain process.

• Appalachians: formed during ancient continental collisions (the Alleghenian orogeny) that folded and thrust rock strata into long ridges -- again a fold-mountain history.

• Ural: formed where the ancient Baltica and Siberian landmasses collided, folding crust along the Europe-Asia boundary into a fold-mountain system.

Of the four ranges, only the Vosges owes its structure to faulting and vertical block uplift rather than plate-collision folding, which is the defining test for a block mountain.