This.Depends on what mean by "old days".
Oyster shells, and Lime was the most common.
On a side note;
The chickens we have to day are nothing like they had in the old days (before poultry feed). Most of today's chickens would be walking skeletons and lay very little eggs if they had to survive solely on free ranging.
Chris
The birds simply didn't lay at the rate they do today, thus needed less calcium. I know my Ozark Grandma fed eggshells back to her birds, and spoiled dairy went to the chicken also. Honestly, they possibly ate a lot more bones than birds today do. But again, Grandma's birds didn't lay near the amount mine do.