I want to know what is the subject of the sentence "A trail of ants marched across the table". Is "trail" the subject or "a trail of ants". Isn't "of ants" an adjectival prepositional phrase? So how can it be the subject? OTOH a trail marching sounds wrong and incomplete. What marched? A trail marched - sounds incomplete. Yet can a prep phrase be a part of a noun phrase? Thanks for your help.