On the 3rd of August an excursion which had been talked of for several days was made into the southeastern part of the island, towards Tadorn Marsh.  The hunters were tempted by the aquatic game which took up their winter quarters there.  Wild duck, snipe, teal and grebe abounded there, and it was agreed that a day should be devoted to an expedition against these birds.

Not only Gideon Spilett and Herbert, but Pencroft and Neb also took part in this excursion.  Cyrus Harding alone, alleging some work as an excuse, did not join them, but remained at Granite House.

The hunters proceeded in the direction of Port Balloon, in order to reach the marsh, after having promised to be back by the evening.  Top and Jup accompanied them.  As soon as they had passed over the Mercy Bridge, the engineer raised it and returned, intending to put into execution a project for the performance of which he wished to be alone.

Now this project was to minutely explore the interior well, the mouth of which was on a level with the passage of Granite House, and which communicated with the sea, since it formerly supplied a way to the waters of the lake.

Why did Top so often run round this opening?  Why did he utter such strange barks when a sort of uneasiness seemed to draw him towards this well?  Why did Jup join Top in a sort of common anxiety?  Had this well branches besides the communication with the sea?  Did it spread towards other parts of the island?  This is what Cyrus Harding wished to know.  He had resolved, therefore, to attempt the exploration of the well during the absence of his companions, and an opportunity for doing so had now presented itself.

It was easy to descend to the bottom of the well by employing the rope ladder which had not been used since the establishment of the lift.  The engineer drew the ladder to the hole, the diameter of which measured nearly six feet, and allowed it to unroll itself after having securely fastened its upper extremity.  Then, having lighted a lantern, taken a revolver, and placed a cutlass in his belt, he began the descent.

The sides were everywhere entire; but points of rock jutted out here and there, and by means of these points it would have been quite possible for an active creature to climb to the mouth of the well.

The engineer remarked this; but although he carefully examined these points by the light of his lantern, he could find no impression, no fracture which could give any reason to suppose that they had either recently or at any former time been used as a staircase.  Cyrus Harding descended deeper, throwing the light of his lantern on all sides.

He saw nothing suspicious.