Since past participles can function as adjectives, every passive construction can be seen as the verb "to be" and a predicate adjective in the form of a past participle.
The apple is red: red is a predicate adjective.
The apple is carried: is carried is a passive construction, and carried is a participial predicate adjective.
Much has been made in the comments of the supposedly incorrect use of carry and alluvium. Carry is used here in the 14th sense defined in the first edition of the Oxford English Dictionary:
to extend or continue (a line, a piece of work) in the same direction to a specified distance, or in a given direction.
There are two other uses of this sense in the same work (The Seven Great Monarchies by George Rawlinson). The first refers to a mine, meaning tunnel:
...he secretly gave orders that the chief efforts of his men should be directed to the formation of a mine, which should be carried under both the walls that defended the place, and enable him to introduce suddenly a body of troops into the very heart of the city.
The second refers to pilasters (an architectural ornament resembling a column):
The exterior ornamentation of the Sassanian buildings was by pilasters, by arched recesses, by cornices, and sometimes by string-courses. An ornamentation at once simple and elegant is that of the lateral faces of the palace at Firuzabad, where long reed-like pilasters are carried from the ground to the cornice, while between them are a series of tall narrow doubly recessed arches.
Alluvium is used here in a sense not found in the Oxford English Dictionary, but it is used in the same sense in one other passage in the book:
The army in Media, favored by the rugged character of the country, was able to maintain its ground without much difficulty; but that which had advanced by the line of the Euphrates and Tigris, and which was still marching through the boundless plains of the great alluvium, found itself suddenly beset by a countless host, commanded by Artaxerxes in person, and, though it struggled gallantly, was overwhelmed and utterly destroyed by the arrows of the terrible Persian bowmen.
Alluvium typically denotes soil deposited by a flooded river, but here it seems to refer to the region in general, as if it were a synonym for "the area of the alluvial plain." The closely related alluvion has senses that support this use; in particular, the legal sense of "land created by flooding" may be intended.