The most widespread type of masonry work is the erection of solid brick masonry using individual bricks set in mortar. âLight masonry,â consisting of two parallel face walls each one-half a brick thick and filled with a light concrete, loose slag, or another insulating material, is sometimes used.
A sinkhole, also known as a cenote, sink, sink-hole, shakehole, swallet, swallow hole, or doline (the different terms for sinkholes are often used interchangeably), is a depression or hole in the ground caused by some form of collapse of the surface layer.
Technically, and by size, the submarine is a ship, but it has been called a boat since its earliest days, and the term is steeped in tradition. Submariners almost invariably call their ships 'boats.  (1) Traditionally vessels small enough to be carried onboard ships were called boats.