The Horseshoe is one of a family of seven-card fortune-telling layouts that circulated in popular card reading manuals, and no author can be assigned to it.
An unattributed layout
Spreads of this kind spread by copying. A layout appears in a cheap handbook, is reprinted in another with the positions slightly altered, and within a few editions has no traceable origin. The Horseshoe is a clear example: versions differ on what the middle positions mean, and none of the versions carries an attribution.
This atlas records the layout it uses and states plainly that the authorship is unknown, rather than assigning it to a period or a person on the strength of the shape.
The shape is the mnemonic
The arc has no function beyond making seven positions easy to lay out and easy to remember in order. A horseshoe is a luck emblem in English folk custom, which is presumably why the name attached itself, but the arrangement would work identically as a row.
What seven positions buy
Seven is enough to separate the situation from what is hidden in it, what obstructs it, what other people are doing about it, and what is advised. That separation is the actual content of the spread. A reader who collapses those into a general impression of the seven cards is not using the layout, and could have drawn one card.