Henry Adam's use of punctuation, “:—”

Question

I've never seen the construction before, except in Spanish for dialogue and Toni Morrison uses a variaton in Beloved, ";—" for denoting a strong pause (well that's we decided in my English class).

How does Henry Adams use ":—"? Is this grammatically correct? How can I incorporate this in my own sentences?

"Among senses, smell was the strongest:—the smell of hot pine-woods and sweet-fern in the scorching summer noon; of new-mown hay; of ploughed earth" - Henry Adams in The Education of Henry Adams

Answer 1

I haven't seen that used before. Reading your example sentence, I treat it just like a regular —. You can probably do whatever you want in your own books, but I would just use —.

Answer 2

Taking a break from typing court orders, and specifically

The Court has sent sealed copies of this Order to: -

Smith & Jones

Brown & Robinson

and the Court of Appeal

I can say that it is used in formal contexts as a strengthened colon: that is, either at the beginning of a list (as in my example), or before an expansion of what has just been said, as in Steve Melnikoff's example. I imagine it is a shortening of viz:- and was later abbreviated to a simple colon.