the tunnel connection was made by a trench. The Commercial National Bank's coal bins were under the sidewalk on Clark Street. There, coal was lifted from the tunnel by a vertical bucket conveyor running in a small shaft. Before the 1940s the tunnels were used to deliver coal to downtown buildings, and to remove ash or clinkers. Trucks began to siphon off significant amounts of business, however, and by the late 1940s, customers began to switch from coal to natural gas to heat their buildings. The ones that kept burning coal switched to delivery by truck because unloading from the surface was easier, and a complex conveyor system was not required. Excavation debris and ashes Early operation in the tunnels was dominated by removal of excavation debris from the tunnel itself, and once tunnel service reached various areas, several construction contractors found that it was less expensive to dump excavation debris down into tunnel trains than it was to haul it out through the congested streets of the Chicago Loop. As a result, excavation debris continued to make up a significant part of tunnel traffic after the tunnel system was completed. Ash from coal-fired furnaces was freely mixed with this stream of debris. In the early days of tunneling, excavation debris was hauled to the surface through small construction shafts and then to the lakefront by horse and wagon. By 1903, some excavation debris was being dumped onto scows for disposal in the lake. In 1904, tunnels sloping up at a 9 percent grade to the Grant Park disposal station were opened, and the vast majority of excavation debris and ash was hauled out to fill Grant Park. A derrick with a boom picked the dump boxes off the cars and swung them out over the lake to dump the fill. The new Cook County Courthouse was among the construction sites that disposed of excavation debris through the tunnel system. Before the digging of the freight tunnels, shallow spread foundations were common using iron grillage to spread the heavy weight where tall buildings were involved. Deep foundations became almost universal with the construction of the tunnel system because the tunnel threatened to undermine shallow foundations, access to the tunnel made it practical to remove large volumes of excavation spoil, and deep basements permitted easy access to the tunnel for coal delivery and ash removal. In 1908, further dumping of refuse