The existence of recesses and of refuse heaps back of the buildings in caves is characteristic of Mesa Verde cliff-dwellings. In the cliff-houses of the Canyon de Chelly and Marsh Pass regions they rarely exist, the house walls being built against the rear wall of the cave, leaving very little space behind them for refuse or fallen débris. This latter feature, due to the geological character of the caves, is also prominent in the cliff-dwellings of the Red Rock country, at the headwaters of the Verde and its tributaries, and is likewise found in a few cliff-houses of the Gila visited by the writer. From one point of view the use of the wall or walls of the cave as house-walls marks a typical form of cliff-dwelling, or a dependent village, distinguished from a cliff-dwelling like Cliff Palace, the walls of which are independent or free on all sides from the cliffs.[37] [Illustration: BUREAU OF AMERICAN ETHNOLOGY BULLETIN 50 PLATE 14 _a._ RELATION IN PARTS OF CIRCULAR AND RECTANGULAR KIVAS 1, 2, 3, 4, 5, banquettes with pilasters thereon; _C. O._ ceremonial opening; _F_, fire-hole; _S_, sipapû (symbolic opening into underworld); _V_, ventilator. _b._ SCAFFOLD HOUSE _A_, large banquette; _C_, adobe roof covering; _D_, deflector; _S_, stick construction supporting roof. DIAGRAM SHOWING KIVA ROOF CONSTRUCTION] The masonry of the Navaho Monument ruins is crude as compared with that found in the ruins of the Mesa Verde National Park, and walls made of adobe supported by upright sticks are more numerous. The character of the masonry may be due in part to the slab-like character of the building stones, and possibly to their greater hardness. The relative predominance of adobe walls supported by upright sticks was fostered by the ease with which they could be constructed and the quantity of clay available for building purposes. Comparison of the masonry of ruins in the Navaho Monument with that of the Black Falls region shows a resemblance much greater than that existing between either group and the cliff-houses of the Mesa Verde region. There is no architectural feature in Southwestern ruins more distinctive than the ceremonial rooms, or kivas, but as these have never been recognized throughout a large area of Arizona, it is important to determine the character of the ceremonial rooms of the Navaho Monument ruins and to compare them with kivas at present used by the Hopi.