"There!" said the foreman. "You've climbed your first ladder. Now we'll see about the shingling."
There was a whole bundle of shingles on the staging, and another bundle that had been opened, 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.