Dear native speakers

In this part of a poem by William Carlos Williams I read
"dog lime". I have no clue what it means and cannot find it by means of internet search. Could anyone know?
Thanks a lot.

"And no one knows
Whether we think good
Or evil.
Then again,
The old man who goes about
Gathering dog lime
Walks in the gutter
Without looking up
And his tread
Is more majestic than
That of the Episcopal minister
Approaching the pulpit
Of a Sunday.
These things
Astonish me beyond words."