GR translation: dripping stone

[Mike Jing]

V679.13-18, P692.19-24   And Los!  the miracle is done, they’re now zipping
along the corridor-streets of the Raketen-Stadt like some long-necked sea
monster.  Little kids boil up like ants on the webby arches of viaducts
high over the city dripping stone like Spanish moss petrified in
mid-collapse, kids up over the airy railings and onto the friendly back of
the sleek city-cruising monster.

Is the "dripping stone" here the same as "dripstone", i.e. a moulding or
cornice over a door, window, etc., to throw off the rain; a label?

Also, does the phrase "like Spanish moss petrified in mid-collapse" modify
"the webby arches of viaducts"?