The third line gave him more trouble; and it was not until some groping that, remembering the position, near the Chambre des Demoiselles, of the Fort de Fréfossé, he ended by almost completely reconstructing the document: _“En aval d’Étretat. La Chambre des Demoiselles. Sous le Fort de Fréfossé. L’Aiguille creuse.”_ These were the four great formulas, the essential and general formulas which you had to know. By means of them, you turned _en aval_, that is to say, below or west of Étretat, entered the Chambre des Demoiselles, in all probability passed under Fort Fréfossé and thus arrived at the Needle. How? By means of the indications and measurements that constituted the fourth line: [Illustration] These were evidently the more special formulas to enable you to find the outlet through which you made your way and the road that led to the Needle. Beautrelet at once presumed—and his surmise was no more than the logical consequence of the document—that, if there really was a direct communication between the land and the obelisk of the Needle, the underground passage must start from the Chambre des Demoiselles, pass under Fort Fréfossé, descend perpendicularly the three hundred feet of cliff and, by means of a tunnel contrived under the rocks of the sea, end at the Hollow Needle. Which was the entrance to the underground passage? Did not the two letters D and F, so plainly cut, point to it and admit to it, with the aid, perhaps, of some ingenious piece of mechanism? The whole of the next morning, Isidore strolled about Étretat and chatted with everybody he met, in order to try and pick up useful information. At last, in the afternoon, he went up the cliff. Disguised as a sailor, he had made himself still younger and, in a pair of trousers too short for him and a fishing jersey, he looked a mere scape-grace of twelve or thirteen. As soon as he entered the cave, he knelt down before the letters. Here a disappointment awaited him. It was no use his striking them, pushing them, manipulating them in every way: they refused to move. And it was not long, in fact, before he became aware that they were really unable to move and that, therefore, they controlled no mechanism. And yet—and yet they must mean something! Inquiries which he had made in the village went to show that no one had ever been able to explain their existence and that the Abbé Cochet, in his valuable little book on Étretat,[8] had also tried in vain to solve this little puzzle. But Isidore knew what the learned Norman archaeologist did not know, namely, that the same two letters figured in the document, on the line containing the indications. Was it a chance coincidence: Impossible. Well, then—? [8] _Les Origines d’Étretat_. The Abbé Cochet seems to conclude, in the end, that the two letters are the initials of a passer-by. The revelations now made prove the fallacy of the theory.