Omit the dash when a colon is used to preface a quotation or similar matter, whether at the end of a break-line or not.
The dash is used to mark an interruption or breaking off in the middle of a sentence.[66]
Marks of Omission.
To mark omitted words three points ... (not asterisks) separated by en quadrats are sufficient; and the practice should be uniform throughout the work. Where full lines are required to mark a large omission, real or imaginary, the spacing between the marks should be increased; but the compositor should in this case also use full points and not asterisks.
Punctuation Marks generally.
The following summary is an attempt to define in few words the meaning and use of punctuation marks (the capitals are only given for emphasis):
A Period marks the end of a sentence.
A Colon is at the transition point of the sentence.
A Semicolon separates different statements.