One student of agriculture has estimated that it would require the whole agricultural population of the United States one hundred days to shell the average corn crop by hand, but this is an exaggeration.
The list of labor-saving machinery in agriculture is by no means exhausted.

There are clover hullers, bean and pea threshers, ensilage cutters, manure spreaders, and dozens of others.

On the dairy farm the cream separator both increases the quantity and improves the quality of the butter and saves time.

Power also drives the churns.

On many farms cows are milked and sheep are sheared by machines and eggs are hatched without hens.
There are, of course, thousands of farms in the country where machinery cannot be used to advantage and where the work is still done entirely or in part in the old ways.
Historians once were fond of marking off the story of the earth and of men upon the earth into distinct periods fixed by definite dates.