How was this formation wrought? In prehistoric times, that is before Iceland was discovered, how much earlier we do not know and the rocks do not reveal the secret save the probable period of the flowing of the lava itself which filled all the valley, the surface cooled and the fluid below this crust was under pressure and forced a passage through the barrier where the lake now lies and drained away. This left a mammoth cavern with a hot, laminated, blistered and shrinking roof. Time passed. The shrinking continued. The stress became sufficient to produce the great fault, an earthquake, and in one mighty tumble the entire roof of the lava chamber collapsed, breaking away from the walls which now form the moorland side of the great parallel rifts. As it fell it was shivered into acre-sized fragments, tilted and turned so as to present a billowy appearance. Time has mercifully clothed the ragged mass with verdure, tangled masses of dwarf birch, which, from the distance of the brink upon which we stand, soften the harsh outlines and partially obscure the chasms. As the roof of the cavern fell it broke away from the mountain walls on either side of the plain and pulled the ragged mass with it. This formed a second wall and between these two walls runs the _Álmannagjá_ on this side of the plain and the _Hrafnagjá_ on yonder side. From the top of the inner walls the slope is gradual down into the plain, much like the inward sloping sides of a platter. On the moorland side enormous niches extend into the wall and protruding from the second wall are masses of lava pulled out of these places which would exactly fit the ancient matrix could they be restored. These are so numerous in each of the rifts that there is no doubt as to the correctness of our view of the formation of the rifts and of _Thingvellir_. Over the brink of the tableland and into the _Álmannagjá_ tumbles a fine sheet of water, the _Öxerá_, Axe-River, which follows the chasm down to a break through the inner wall, spreads over a portion of the plain and enters the lake. At our feet there is a narrow side passage leading from the brink down into the rift which has been laboriously levelled and a good road now leads to the lower level. This pass in ancient days was the strategic point of many a stout fight. In the _Burnt Njal_ we read a vivid description of such a fight when the issue of the trial was unfavorable to one of the factions. We will now ride down the incline, cross the bridge over the foaming _Öxerá_ and draw rein at the _Valhöll_, Great-Hall-of-the-King. This was erected when King Frederick of Denmark visited the place in 1907. That the good king toured a portion of Iceland at this time is a blessing to travellers because special roads were built, bridges erected and inns constructed for his accommodation.