North of Chateau-Thierry, three or four kilometres from the Marne, the plateau is less diversified. The only obstacle is the valley of the Clignon, which deepens rapidly toward the west. Above it, at the summit of the limestone cliff, the plateau forms a species of promontories on which are built villages--Torcy, Belleau, Bouresches. The American troops had held their positions there during the last part of June, and it was there that the heroic marines halted the enemy in his march upon Paris. And again, it was there that they assumed the offensive on July 18, to outflank Chateau-Thierry from the north. On that day they carried the ridges of Torcy and Belleau; on the 19th they pressed beyond Bouresches; and on the 20th they forced their way into Etrepilly and Chateau-Thierry. [Sidenote: The terrain beyond is less rugged.] Immediately beyond, the terrain is not so difficult. The Clignon valley becomes less rugged and gradually blends with the plateau. Toward Bezu-St.-Germain and Epieds lies a comparatively open plain with extensive stretches of fallow land. In this more open region the progress was more rapid; on July 22 the American troops took possession of Epieds, twelve kilometres from Bouresches, their starting point. [Sidenote: Along the valley of the Ourcq.] But the difficulties are more serious farther to the north, along the hills which form the southern boundary of the valley of the Ourcq. Although the depression made by the Ru d'Alland, being broad and level, is not a considerable obstacle, it is not the same beyond. The relief map shows a line of heights running from west to east, and rising higher and higher in that direction. From these heights a multitude of valleys descend to the Ourcq, from south to north, cutting the crest into hills separated by depressions. Thus the terrain is broken up in every direction and well adapted to meet an attack from the west as well as one from the south. [Sidenote: The French carry ridges and valleys in succession.] It was necessary to deal with all these obstacles one by one. Starting from the west, the French had to carry successively these lines of crests and depressions with their fortified villages: ridge of Monnes, July 19; ravine of Neuilly-St-Front the same evening; the hill of Latilly and its wood the 20th; La Croix and Grisolles the 21st, with their thickets and dense plantations of osiers. On the 23d the Allied troops took Rocourt and the wood of Le Chatelet; on the 24th the deep ravine of Brecy; and, finally, on the 25th, French and Americans together attacked the hill of the forest of Fere, which is 228 metres high, completely covered with woods, cut by ravines, and flanked by fortified villages. On the 27th the whole position was taken, and the Allies were on the verge of the deep valley of the Ourcq, which they were next to cross. [Sidenote: Caves in the cliffs.] [Sidenote: Allies turn the line of the Ourcq.]