Zuñi plateaus, Dutton describes numerous relatively small isolated buttes or sharply conical hills, steeper sided than volcanic cones, of a different profile, and without the crater at the top. They consist of dense lava, not in layers spread out from a central vent upon the surrounding surface, but in a solid mass with 
Fig. 4. columnar structure; and at their bases it is sometimes possible to see that they are inclosed on all sides by the country rock. It is believed that these buttes are nothing more than lava-plugs, frozen solid in the pipes up through which the lava rose at the time of eruption from its deep source to the surface where it overflowed; but that the time of eruption is so long ago that the cones and all the surface outpourings are worn away, and only the stumps of the plugs remain to tell the tale. Fig. 6 attempts to show the early and late forms, one below the other. Structures 
Fig. 5. of the same kind are known in the Black Hills, in Scotland, and elsewhere. Perhaps this hint will help us in understanding Connecticut.
There is one thing about the ash-bed and lava-sheets in Connecticut that is certainly favorable to the suggestion given by the Zuñi buttes. The lava-sheets are not now level, as they undoubtedly were when they were poured out; but all the series of sandstones, ash-beds, lava-sheets, and the rest have been lifted up together on the western side of the valley, so that they slant down or dip to the eastward at a moderate angle. Standing on the bluff of the ash-bed, it is easy to trace its edge north and south, and to perceive that it is continued slanting underground on the east, and to imagine that it was once continued upward into the air on the west; for on this side the uplifting exposed it to the patient, persistent attack of the weather, by which in the course of ages it may have been greatly worn away. In the same way, other lava-ridges in the neighborhood, such as Mount Lamentation and the beautiful Hanging Hills, are simply the worn edges of lava-sheets that still plunge underground eastward, and that once rose high into the air westward.
It follows from this new understanding that if the vent, from which the ashes were blown and the lavas poured, lay to the east
