The finest aboriginal pipes are unquestionably the so-called monitor pipes found in the Ohio mounds. Many of these show such excellence of design and execution that early investigators doubted whether they could be the work of American Indians. They are made of soft stone or of fire clay, which was carved like stone, but never of pottery. The type is characterized by a long, broad, and very thin base from the center of which the bowl rises vertically. The base may be either flat or convex. The bowl is often made in the form of an animal or bird, and some of these effigies show artistic ability of a high order. Even when the style is impressionistic, the species is usually unmistakable. The significance of these carvings can only be conjectured, but so many species are shown that it seems probable that they represent the personal guardians of the pipes’ owners. None of the historic tribes used pipes of this type, and the finest examples are unquestionably pre-Columbian. One of the pipes illustrated (Pl. IV, No. 1) is of typical monitor form, but has the bowl incised with designs representing bird’s heads. In the other (Pl. IV, No. 2) the shape has been modified to suit the subject, a roseate spoonbill resting on the back of some large water animal, probably a mud puppy (_Necturus maculosus_). A number of large stone pipes have been found in the southeastern United States (Pl. III, Nos. 4–5). Some of these pipes weigh several pounds and, as they are everywhere associated with smaller forms of stone or clay, they were probably made for ceremonial use. They seem to have been provided with long, thick wooden stems. These heavy pipes are of several types, and are usually well made, but are inferior to the monitor pipes in design and execution. In Georgia, Alabama, and the lower Mississippi valley there is a very massive short type in which the bowl and stem holes are conical and of nearly equal size and depth. These biconical pipes are often made in the form of human effigies or of highly conventionalized animals or birds. Early visitors to the north Atlantic Coast say that the Indians of that region used heavy carved pipes with stems three to six feet long. Large stone pipes are hardly ever found in this region, and even small carved pipes are extremely rare. It seems probable that these early forms either had quite small, plain bowls with heavy carved stems, or were made of wood or other perishable material. Holm says that the Pennsylvania Indians made their pipe bowls of horn, and several of the Algonquian tribes have made a considerable use of carved wooden pipes in historic times. Among many tribes the stems of ceremonial pipes were elaborately decorated, and were considered more important than the bowls.