The cliffs above Dover Harbour have quite an interesting history. Apart from the mineral railway, which lowered material to sea level by an incline located between the first two groups of bushes on the right of Imageo's photo (the last in his album), the downward sloping line seen in the same photo was reputed to have been excavated for the proposed Dover to St Margaret's/Martin Mill extension of the 3' 6" guage electric tramway system.
The whole system was taken over by the military in the last war and extended with numerous branches serving fixed gun emplacements and protected areas for the big rail mounted guns, complete with n.g. systems for ammo storage.
So we don't forget this website's about mines, there was an aerial ropeway from Tilmanstone Colliery to the Eastern Arm of Dover Harbour (almost directly below the camera in the photo) which ran in twin tunnels through the cliffs to reach the loading berths. For the record, I believe Tilmanstone had seams at 3000', 6000' and 12000' below surface level, the last was never worked. The shafts have been plugged with some 35,000,000 tons of high quality coal still underground over the whole coalfield.