Coring tubes are best adapted for sampling fine-grained sediments (clays and fine silts). Since most coring tubes penetrate to a greater depth than other types of samplers and preserve a little-disturbed section of the bottom, they are to be preferred for work on fine-grained sediment. Trask's modified Ekman coring tube, constructed of ordinary plumbing stock, is perhaps best suited to the requirements of most investigations because of its low cost and simplicity of construction and operation. A pile-driver type of coring tube, similar to that described by Twenhofel, makes possible the collection of longer cores in water up to 100 feet deep. The Davis peat sampler is very satisfactory for water less than 40 feet deep. For the collection of longer cores in deep water, inst uments such as the Piggot gun or perhaps the Varney-Redwine hydraulic apparatus, if it can be developed satisfactorily, must be used.

Clamshell samplers, of the Ross and Fish-Hawk types, are probably most generally used for the collection of coarser sediments in the range from coarse silt to fine gravel. These are comparatively inexpensive, and may be used by hand in shallow water if desired. They have the defect, however, of sometimes losing the finer material if a large grain is caught in the jaws. The Stetson-Iselin sampler is most satisfactory for the sandy sediments and may be used to collect finer-grained material if core samples are not desired. This instrument is comparatively costly and it must be used with a hoisting rig. The dwarf orange-peel bucket, also costly, takes a large sample and will pick up large-sized particles. It may be used by hand, in shallow water, if no hoisting machinery is available. Th s sampler should prove satisfactory for a variety of sediments, if provided with a hood to protect the sample from washing.

Drag buckets or dredges, instruments which are towed along the bottom, are not recommended for the collection of material finer than gravel, because several of the instruments that have been described are better suited for that work. The main advantage of the ordinary drag bucket or dredge is its low cost and simplicity of design. Drags are very useful for certain specialized sampling, such as the collection of bedrock samples from the sides of canyons in the Continental Shelf. Apparatus such as Stetson's modified Mann sampler will collect coarse sedimentary particles that cannot be secured with coring tubes or the smaller grab buckets, but the Petersen "dredge" and the dwarf orange-peel bucket, both of which are large grab buckets, will perform the same task and they can be used at a y depth.