This sentence is a compound-complex sentence composed of two independent clauses joined by the coordinating conjunction and along with a dependent clause (acting as an adjective clause)
1st independent clause:
Inquiry was made into the origin of the scourge [Subject: inquiry Predicate: was made]
2nd independent clause:
by degrees various facts came out [Subject: facts Predicate: came out]
The dependent clause:
which excited public indignation in a high degree.
[Subject: which Predicate: excited] (which is a relative pronoun that begins the adjective clause that modifies the word facts.)
- Please note that "into the origin of the scourge" are only two prepositional phrases that belong in the first independent clause. They are NOT a dependent clause because a clause, by definition, has a subject and a predicate.
There is a site below that lists prepositions among which are into and of.