For hundreds, if not thousands, of years, mariners used leadlines to determine the depth of water. Knowing the depth would tell if the ship was or was not in danger of grounding. Many lead weights on the end the leadlines had a depression filled with wax or paraffin. When the lead struck the seafloor, some of the bottom material would become embedded in the wax or paraffin. When the leadline was raised, examination of the retained material could sometimes give the master additional information regarding the ship’s position, as charts often show the prevalent bottom composition in each area. Leadlines were considered a vital piece of equipment on the ship and the ship might be considered unseaworthy if it sailed without one. Merchant ships generally carried two types of leadlines: a deep sea leadline of about 100 fathoms length with the lead weighing 28 pounds or more and a hand leadline of about 25 fathoms length with the lead weighing 14 pounds or less. To avoid having to measure the length of line after each throw, it became traditional to tie marks at intervals along the line. The marks were made of different materials and had different shapes so that they could be easily recognized by appearance or feel. If the depth indicated by the leadline was at a mark, the leadsman would call out “by the mark” followed by the depth. If the depth was between two marks, the leadsman would call out “by the deep” followed by the estimated depth. Sometimes, particularly on the Mississippi and Ohio Rivers, leadsmen would use the word “twain” rather than “two” when reporting the depth. Thus, a depth of two fathoms might be called out as “by the mark twain”. The author Samuel Clemens, who worked as a river pilot in his youth, allegedly took his pen name from this practice. With the development of fathometers, use of the leadline gradually disappeared. It was not until 1996, though, that the US Coast Guard (not being a slave to fashion) finally amended its regulations to eliminate the requirement for carriage of leadlines by most US ships.