South and southwest of Lens the Canadians continued to fight hard and to make important gains. They succeeded in getting a firm grip on a stronghold only 300 yards south of the main railway station of the town. This was a huge slag pile which had been tunneled by the Germans and was known as "Green Crassier." The odd position constituted a barrier between the Canadians and the defenses of the city proper. It was connected by tunnels with dugouts and defenses underneath Lens, and the Germans, appreciating its value, clung to it tenaciously. Preceded by a heavy bombardment the Canadians attacked at early dawn and were atop of the Germans before the latter had any warning of what was impending. The long series of counterattacks in which they had been engaged during the previous days had not entirely quenched the German fighting spirit, and the slag pile was such a network of defenses that the Canadians were from the start roughly handled, but they held on with dogged determination, though they had never faced more formidable conditions, and despite the desperate efforts of the Germans to oust them. Surrounding the slag pile or "crassier" many of the ruined buildings had been transformed into strong and most ingeniously constructed fortifications. The Canadians systematically bombed their way through these defenses and drove out the defenders, who sought refuge in the numerous tunnels under the city. Lens was crowded with German troops of the Fourth Guards Division and the First Guards Reserve. Forced to live among the dead and wounded in underground caves, their lot was hideous beyond description. French troops operating in the Verdun sector gained an important victory on August 24, 1917. In the early morning they began a powerful offensive on the left bank of the Meuse between Avocourt Wood and Dead Man Hill. By a single charge they carried Hill 304 and Camard Wood to the west of it. All the German positions were captured and the defenders made prisoners. To make doubly secure their possession of Hill 304, the French pushed on beyond it for a distance of about a mile and a quarter. The loss of Hill 304 and Dead Man Hill, which commanded all the approaches and ravines as far as Douaumont, deprived the Germans of every observation point from which they could watch the operations of the French troops.