“Got the flash-lamps, inspector?” Sir Clinton demanded as he pulled up the car at a point considerably beyond Neptune's Seat. “That's all right. We get out here, I think. We ought to be opposite those two cairns we built, if I'm not out in my reckoning.”
They moved down the beach and soon came to a long pool of sea-water extending into the darkness on either hand. Sir Clinton surveyed it for a moment.
“We'll just have to splash through, I suppose,” he said, and set an example. “It won't take you over your ankles.”
A few seconds took them through the shallow pool and brought them to drying sands on the farther side.
“This is a low whale-back,” Sir Clinton pointed out. “When the tide's full in, this is covered, like all the rest. Then, as the tide falls, the whale-back acts as a dam and there's a big sea-pool left on the sands between here and the road. That's the pool we've just waded through. Now we'll look for the next item.” Wendover and Armadale followed him across the sands to where a broad stream of water was pouring down towards the sea.
“This is the channel between our whale-back and the next one,” Sir Clinton explained as they came up to it. “This water comes from the pool that we waded; and the cairns are on each side of it, lower down.”
The night was cloudy, and they had to use their flash-lamps from time to time.
“What I wanted to note is the exact time when the stream just touches the cairns on each side. Just now, as you can see, the cairns are in the water; but the level of the stream's sinking as the head of water falls in the pool behind. Watch till the stream runs between the two piles of stone and then note the time.”
Slowly the flow diminished as the water emptied itself from the pool behind; and at last they saw the rivulet confined to a channel between the two cairns.
“I make it five past twelve,” Sir Clinton said, lifting his eyes from his watch. “Now I'm going over to Neptune's Seat. You stay here, inspector; and when you see my flash-lamp, run your hardest to the rock and join me.”