Please post an image of the entire cover.
I think that 'patent cancels' were first used in NY and were called "cutter" cancellations. Here is a letter from NY Postmaster Abram Wakeman to the Third Assistant Postmaster General A. N. Zevely in Washington, DC.
Post Office New York,
January 3, 1863
Sir: Some time since you requested that I should test the utility of Norton's double post-marking and cancelling
stamping iron, and report my opinion thereon. It was in use in this office when I first entered upon my duties.
Since then the cancelling part has been changed in various forms. We have tried the cutter thoroughly. This is the
most complete method of cancellation; but it is liable, even if used with the greatest care, to injure the contents of
the envelope, especially if the enclosures are cards, photographs, and the like. We have also used cork, by inserting
it in the cylinder of the canceller. This has proved successful, and our cancellation is now performed in this way.
I am confident no office in the country performs cancellation more thoroughly.
The design of Mr. Norton is indispensable to us. Indeed, unless I should nearly double the stamping force, we
could not dispense with its use. I am satisfied the interest of the department would be subserved by securing its
We are now testing a stamp and canceller on Norton's plan, made of boxwood. It promises well, and can be
made at a very trifling expense. I am fearful, however, its liability to yield to the wear to which it will be subject
may prevent its general adoption. Time will determine this.
Very respectfully, your obedient servant,
ABRAM WAKEMAN, Postmaster
These were 'blade' kind of cuts in the stamp like this
As SPQR mentions, other types/styles were tried in the the years that follow.