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Bafall. 457 ffumbling-block ia the way of this theory, and, indeed, of every other, is the difficulty of ac- counting for the regulär formation of the prifms. It, however, is much eafier accounted for in this fyftem than in the volcanic, as we can pro- duce many inftances of fimilar prifms in fofiils undoubtedly formed in the moift way, and none at all of any undoubtedly formed in the dry. This form feems to me to proceed from the fudden burfting of bafaltic maifes, whether from drying, or the abforption of air, I Ihall not decide. This opinion is founded on the following reafons: ift, ln a heap of ftones of the fpecieb called, in Dublin, Black %uarry-flone, extrafled from a quarry near Palmerftown, and dclcribed in my Elements of Mineralogy under the name of Calp, Mr. Gandon, the celebrated architeft of moft of our public edifices, difcovered one lying under feveral others in the area of the Cuftom-houfe, which had burlt lince it was brought there into regulär pillars, fome of an hexagonal, and fome of an oftagonal form, and fome articulated ex- a&ly like the pillars of the Giant’s Caufeway. Thefe pillars were at firft about fix inches long, and one fourth of an inch in diameter, but after- wards accidentally broken when removed to his apartment; in'this ftate I have feen them. One of our commiffioners of the rcvcnue faw them before their removal. This Hone refembles ba- falt fomewhat in its compolition, but contains a ntuch karger proportion of calcareous carth, and a much fmaller of iron. 2d, Mr. Dolomieu, in the province of Vola- terra, found micaceous marls to aflume a prif- matic form on drying. Near Cape del Bove he , found