ned, and the shingle men had thrown a good
many of these shingles up on the roof, so that they would be handy.

And David saw that there were three rows of shingles on already, and
that a string was stretched tight across the last row; and the string
was chalky-looking, and blue.

"They're just going to mark another row," the foreman said. "You
watch."

Then one of the shingle men lifted the stretched string between his
thumb and his forefinger, and he let it go, and it snapped down hard
upon the shingles.

And they took the string away, and there was a blue line all along the
row of shingles.

"What is that?" David asked.

"Chalk, Davie. They put chalk on the string by rubbing a lump of chalk
on it. That line shows where the edge of the next row of shingles goes.

"And they lay the shingles on so that each crack in the row beneath is
covered. The shingles are different widths, you see, and they can
always find one that fits up close to the next one and covers a crack.

"If the cracks were not covered, the rain would get through and the
roof would leak.

"Now let's see if you can lay shingles. Pick out one that you think
will be right to cover the crack in the row beneath, and lay it down
close up to the last one and with its thick edge to that blue line."

David was rather excited at the thought that he was to lay the
shingles.

"Shall I?" he asked.

The foreman nodded, and he pointed to a shingle.

"Try that one."

So David took the one that the foreman pointed at, and he laid it down
as well as he could, close up to the last one which the shingle man
had put on, and with its thick edge at the blue line.

It took him some time, because he had never laid shingles before; but
the shingle man had only to change it a tiny bit, and then he drove in
two nails about halfway up toward the thin edge.

And David took another shingle which the foreman pointed at, and he
fitted it in its place a little more quickly, and the shingle man
didn't have to change that one at all, but drove the nails with hardly
more than two blows of his hammer.

So David kept on laying shingles, and the shingle man nailed them.

At first the foreman pointed to the right shingles; but, after a while,
he didn't point, but David chose them himself.

And they finished that row, and they began the next.

"I'm afraid, Davie," the foreman said, "that we'll have to go down
now. Aren't you ready to go?"

David was getting a little b