An astounding number of emails about my recollection of “best thing since [dung] came off the shovel” as a predecessor to “…since sliced bread.” This reader gets most of it:

“Dear Derb—I hadn’t heard this expression, but that doesn’t stop me from theorizing. … It is said that Lincoln was disappointed with the reception given the Gettysburg Address and told a friend immediately afterwards that the speech ‘won’t scour.’ This may be a myth, like the story of him drafting the speech on the back of an envelope, or it may have really happened, but it is the kind of metaphor drawn from rural life that Lincoln often used.

“Plowing a field with a plow pulled by a draft animal is a really hard job, but it is somewhat easier if the plow will scour, i.e. if the soil comes cleanly off of the surface. The shape of the blade, the surface of the metal, or the composition of the soil may keep the plow from scouring. It is a real burden if the farmer has to stop every few feet to clean the plow off.

“The John Deere company describes the achievement of its founder in developing a self-scouring plow that worked better in the soil of Lincoln’s midwest than did the older designs used in the East.

“Shoveling a load of stuff is another lousy job, especially if it is the stuff referred to in your idiom, but at least you can get into a rhythmn if each shovelful of what you are digging comes off the blade easily. If you have to stop to knock the shovel against a hard surface, push the stuff off with another tool, or (worse still) with your hand or foot, the bad job becomes far worse.

“You might be better off using a pitchfork for the stuff in question but there is precedent for the use of shovels (See George C. Scott’s opening speech in Patton). Just as the self-scouring steel plow was a big improvement over its predecessors, a shovel blade that allowed the material to slide off easily would be a great boon to those doing the shoveling. Maybe enough of a boon to deserve becoming a proverb. Especially with that alliteration you bowdlerized.”