I was now arrived at the head of this lovely vale, at the sources of the river Moselle and the base of the great mountain the Ballon d'Alsace, which closes it in like a wall at the end of a lane. For some miles past the hills had grown higher and higher upon either side, the valley floor narrower, the torrent less abundant; there now stood up before me the marshy slopes and the enormous forests of pine that forbid a passage south. Up through these the main road has been pierced, tortuous and at an even gradient mile after mile to the very top of the hill; for the Ballon d'Alsace is so shaped that it is impossible for the Moselle valley to communicate with the Gap of Belfort save by some track right over its summit. For it is a mountain with spurs like a star, and where mountains of this kind block the end of main valleys it becomes necessary for the road leading up and out of the valley to go over their highest point, since any other road over the passes or shoulders would involve a second climb to reach the country beyond. The reason of this, my little map here, where the dark stands for the valley and the light for the high places, will show better than a long description. Not that this map is of the Ballon d'Alsace in particular, but only of the type of hill I mean. Since, in crossing a range, it is usually possible to find a low point suitable for surmounting it, such summit roads are rare, but when one does get them they are the finest travel in the world, for they furnish at one point (that is, at the summit) what ordinary roads going through passes can never give you: a moment of domination. From their climax you look over the whole world, and you feel your journey to be adventurous and your advance to have taken some great definite step from one province and people to another.