Caverns are met with in mountains, and few or none in plains: there are many in the Archipelago, and in other islands, because they are in general only the tops of mountains: caverns are formed like precipices, by the sinking of rocks, or large abysses, by the action of the fire; for to make a cavern form a precipice or abyss, we need only suppose the tops of adjacent rocks had fallen together and formed an arch, which must often happen when their bottoms are shaken and dislodged by time or earthquakes. Caverns may be produced by the same causes which produce holes, the shaking and sinking of the earth, and which causes are the explosion of volcanos, the action of subterraneous vapours and earthquakes; for they occasion caverns, holes, and hollows of every kind by their shocks and commotion. St. Patrick's cavern in Ireland is not so considerable as it is famous; it is the same with the Dog's Grotto in Italy; and that which throws out fire, in the mountain of Beniguazeval in the kingdom of Fez. In the county of Derby, in England, there is a very considerable cavern, much larger than the famous cavern of Beauman, near the Black Forest, in Brunswick. I have been informed by a person as respectable for his merit as his name, Lord Morton, that this large cavern, called the Devil's Hole, at first presents a very considerable opening, larger than any church door; that through this opening a rivulet flows; that in advancing the vault of the cavern becomes so low, that persons who are desirous of continuing their road are obliged to lie flat in a boat and be pushed through this narrow passage, where the water almost touches the roof; but after having passed this part of the vault, the arch rises to a considerable height, and continues so for some distance, when it sinks again so low as to touch the water, and where the cavern ends. The source of the rivulet which issues from it sometimes encreases considerably: it transports and heaps up a great quantity of sand in one part of the cavern, which is formed like a kind of alley, whose direction is different from that of the principal cavern. In Carniola, near Potpechio, is a very spacious cavern, in which is a large lake. Near Adelsperg is a cavern, in which we may travel two German miles, and where very deep precipices are to be met with.[AF] There are also large caverns and beautiful grottos under the mountains of Mendip, in Wales; mines of lead are found near these caverns, and whole oaks at fifteen fathoms deep. In the county of Gloucester there is a very large cavern, called Pen Park-hole, at the bottom of which there is thirty fathoms water, and mines of lead are also found. [AF] See Act. erud. Lips. anno. 1689, page 558. The Devil's Hole, and other caverns, from whence issue large springs or rivulets, have plainly therefore been formed by the water, and their origin cannot be considered as the effects either of earthquakes or volcanos.