_a a._ stratified basaltic scoriæ. _b b._ Bands made up of fragments of burnt slate. _c._ Stratified basaltic scoriæ. _d d._ Pseudo-dykes occupying lines of fault.] [Sidenote: ARRANGEMENT OF FRAGMENTAL MATERIALS.] If, in consequence of any subterranean movements, fissures are produced in the sides of the cones formed of fragmentary materials, these often become gradually filled with loose fragments from the sides of the fissure, and in this manner 'pseudo-dykes' are formed. An example of such pseudo-dykes is represented in fig. 36, where the beds composing the volcanic cone of the Kammerbühl are seen to have been broken across or faulted, and the fissures produced in the mass have been gradually filled with loose fragments. It is not difficult to imitate, on a small scale, the conditions which exist at those volcanic vents from which only fragmentary materials are ejected. If we take a board having a hole in its centre, into which a pipe is inserted conveying a strong air-blast, we shall, by introducing some light material like bran or sawdust into this pipe cause an ejection of fragments, which will, when the board is placed horizontally, fall around the orifice of the pipe and accumulate there in a conical heap (fig. 37). It will be found necessary, as was shown by Mr. Woodward, who performed the experiment before the Physical Society, to adopt some contrivance, such as a screw, for forcing the material into the air-pipe. If we alternately introduce materials of different colours, like mahogany- and deal-sawdust into the pipe, these materials will be arranged in layers which can be easily recognised, and the mode of accumulation of the mass will be evident. By means of a sheet of tin or cardboard we may divide this miniature volcanic cone vertically into two portions, and if we sweep one of these away the internal structure of the other half will be clearly displayed before our eyes. In this way we shall find that the conical heap of sawdust with the hole in its centre has a very peculiar and definite arrangement of its materials. It is made up of a number of layers each of which slopes in opposite directions, towards the centre of ejection and away from that centre. These layers are thickest along the line of the circle where the change in slope takes place, and they thin away in the direction of the two opposite slopes. [Illustration: Fig. 37.--Experimental illustration of the mode of Formation of Volcanic Cones composed of fragmental materials.] [Sidenote: CAUSE OF THIS ARRANGEMENT.]