This photograph shows two headings (tunnels) that was much the same in design. The first section of the tunnel is seen to be under great pressure with the roofing timbers (collars) and uprights (arms) bending and breaking This situation was due to a great weight being applied from both above, and sides. The second picture shows a section of heading that is handling the weight much better; this is due to the structure being made up of rock and solid strata. Of course, cutting a tunnel through this type of strata would be time consuming and exhausting.   Depending on the type of roof, whether firm or loose strata, more or less timber would be needed. The timber used was usually Norway fir. These were the best because when under strain from the weight, they gave off sounds of creaking and cracking, thus giving miners a warning that extra caution was needed. Unlike hardwood timber that would suddenly snap without warning, this type of fir was tough and stringy, rather than hard and brittle.