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 EVIDENCE OF SUBMERGENCE 23 a depth of 1 ,700 fathoms, where the grappling irons of a cable- mending ship dragged for several days over a mountainous sur- face of peaks and pinnacles, bringing up "little mineral splinters" evidently "detached from a bare rock, an actual outcropping sharp-edged and angular." These fragments were all of a non- crystalline vitreous lava called tachylyte, which "could solidify into this condition only under atmospheric pressure." He infers that the territory in question was covered with lava flows while it was still above water and subsequently descended to its present depth; also from the general condition of the rock surface that the caving in followed very closely on the emission of the lavas and that this collapse was sudden. He thinks, therefore, "that the entire region north of the Azores and perhaps the very region of the Azores, of which they may be only the visible ruins, was very recently submerged, probably during the epoch which the geologists call the present." He believes also that like results would follow a "detailed dredging to the south and the southwest of these islands." 16 It will be observed that the whole of this very tempting edifice is built on the declared impossibility of tachylyte forming on the sea bottom under heavy water pressure. But Professor Schuchert insists that: "It is not pressure so much as it is a quick loss of temperature that brings about the vitreous structure in lava. In other words, vitreous lava apparently can be formed as well in the ocean depths as on the lands. What the cable layers got was probably the superficial glassy crust of probable subter- ranean lava flows." 17 If that be so, there is, of course, no need to infer a descent of territory into the depths in that region of the mid-Atlantic. This tachylyte matter seems enveloped in uncer- tainty. On the other hand, it is well known that volcanic outbursts and earthquakes have been rather frequent and alarming even in modern times among the islands of the eastern Atlantic archi- pelagoes, especially the Canaries and the lowest and middle 18 Termier, pp. 226 and 227. " Ceogr. Rev., Vol. 3, iQi?, p. 66.