It was time for the “cementing off,” to make the well water-proof, and protect the precious oil-sands. Down there under the ground was a pool of oil, caught under a layer of impermeable rock, exactly like an inverted wash-basin. The oil was full of gas, which made the pressure. Now you had drilled a hole through the wash-basin, and the oil and gas would come to you—but only on condition that you did not let any surface water down to kill the pressure. All the way down you had been tapping underground streams and pools of water; and now you had to set a big block of cement at the bottom of the hole, solid and tight, filling every crevice, both inside and outside your casing. Having got this tight, you would drill a hole through it, and on down into the oil-sands, thus making a channel through which the oil could flow up, and no water could leak down. This was the critical part of your operation, and while it was going on the whole crew was keyed up, and the owner and his son, needless to say. First you put down your casing, known as the “water-string.” If you were a careful man, like Dad, you ran this “string” all the way up to your derrick-floor. Next you began pumping down clean water; for many hours you pumped, until you had washed the dirt and oil out of the hole; and then you were ready for the cement-men. They came with a truck, a complete outfit on wheels, ready to travel to any well. Another truck brought the sacks of cement, a couple of hundred of them; the job called for pure cement, no sand. They got everything ready before they started, and then they worked like so many fiends—for this whole job had to be put through in less than an hour, before the cement began to set. It was an ingenious scheme they had, very fascinating to watch. They fitted inside the casing a cast-iron “packer,” having rubber discs at the top and bottom, so that it floated on the water in the casing; the cement went on top of this. The sacks were jerked open, and dumped into the hopper of the mixing machine, and the mixer began to revolve, and the river of grey liquid to pour into the hole. It ran fast, and the heavy pumps set to work, and drove it down, stroke after stroke. In half an hour they had filled several hundred feet of the casing with cement; after which they put on a rubber “packer,” fitting tight to the casing; and again the heavy pumps went to work, and drove the mass of cement, between the two “packers,” down into the hole. When they came to the bottom, the bottom packer would drop, and the cement would pour in, and the pressure of the top packer would force it into every cranny of the hole, and up between the outside of the casing and the earth—one or two hundred feet high it would rise, and when it set, there you would have your “water shut-off.”