Deposits, such as coal, tar sand, heavy crude oil and/or minerals are excavated from an underground formation layer (4) by:—inserting a chain cutter string (11) into a 1st section (8, 9) and a control cable (12) into a 2nd section (10) of a T-, V-, U-, or L-shaped channel assembly (8, 9, 10) traversing the layer (4);—connecting the control cable (12) to the chain cutter string (11) at a branchpoint (13) of said 1st & 2nd sections (8, 9 & 10); and—pulling the chain cutter string (11) in a continuous or oscillating manner through the first section (8,9) while continuously pulling the control cable (12), such that the chain cutter string (11) carves deposits from the layer (4) and the control cable (12) optimizes the performance and reduces the risk of breakage of the chain cutter string (11).