“We are thus led to believe that as between the West Indian terranes and the neck of land now embraced in the Isthmus of Panama, we have a relation of Isostacy.’”
The speaker, armed with this formidable verbal equipment of attack upon his audience, had walked to the front of the platform, and, harboring some unusual confidence in his powers, had deserted his manuscript. Isostacy, he had realized, possessed probably unqualified novelty, and by way of assurance, lest its terrors might empty the hall, he assumed a colloquial relation to his dazed hearers, and offered an explanation of this unexpected mystery. “Isostacy,” he resumed, “is simply this: Equilibrium. It is the maintenance of average level—as if one part of the earth’s surface was pushed up, above a mean level, then the requirements of Isostacy would depress another part, below it. We can also call it the adjustment of a changing load, as if through depression, from the dumping upon the floor of the ocean of a great amount of sediment, derived from the land surface of the earth, neighboring areas of the land of the oceanic floors were raised. Two contiguous regions might—and,” the lecturer turned directly toward the President, who in his own earnestness of attention had elbowed himself round into a direct line with Mr. Binn, “in the case of the West Indian continent and the Isthmus of Panama, have maintained between them, an up and down reciprocity of movement, as, when one was up, the other was down, and vice versa.”
Mr. Binn looked introspectively at the walls and ceilings of the room, as if engaged in a mental rehearsal and review of his staggering statement, and returned to his desk and manuscript, satisfied that he had thrown the assembly into an uneasy apprehension of danger. He again began his reading: “It is true, if I understand Mr. Spencer correctly, that the Atlantic ocean was cut off by the elevation of the Columbian Continent from even the interior basins of the Caribbean Sea and the Gulf of Mexico, at least in early pliocene times; that these depressions were then broad plains receiving in part the drainage of the Antillean highlands; this again emptying into the Pacific ocean. But this is not a proven theory, and it involves an extravagant readjustment of the physical features of a region that to my mind more expressively can be considered immemorially permanent, in their general aspects, at least. I reiterate the reciprocity of movement between the Antillean Continent and the Isthmus of Panama. The cause I have suggested may be untenable—but there seems strong geological proof of some such alternating relation between the west and east sides of this inter-related region, the Great Antilles on one side, the Isthmus of Central America on the other.
“Our survey of the question produces one impression, and that very forcibly, viz.: that this narrow ridge of separation is ephemeral, that it is perishable, that under the tests or against the shocks of earth strains, it will succumb, and”—the lecturer raised his voice, half turned deferentially to the chairman, Dr. Smith, who accepted the attention with an assenting nod—“again the waters of the two oceans will unite, and the impetuous violence of the rushing oceanic river, the Gulf Stream, that now races and boils through the Caribbean Sea, will fling its torrential waves across this divide into the Pacific.”
The audience that with manifest absorption had thus far followed the speaker, was disturbed. A movement of chairs, a half audible protest of whispered incredulity, and a sensible emanation around him, of mental repugnance to such a catastrophe, made Leacraft momentarily turn his eyes from Mr. Binn to the frowning countenances at his side.
“But,” the speaker raised his voice with reassuring quickness, as if to stay the emotional resistance he had aroused, “we have no reason to believe that in our lifetime, or the lifetimes of many generations yet to come, so strange a reversal of present conditions should occur. And again, that in this matter, we may be calmly judicial, we have reason at least for a moderate fear. Whatever state of unstable equilibrium, of unadjusted balance is implied, or actually is resident in this section of our earth, a section that has undergone the extremes of hypsometrical displacement, we may conceive that like the explosive cap, or the compressed spring, or the bent bow, it will win instant relief upon the impact of any force, deep-seated enough, and powerful enough, to liberate its tectonic strain.
“I am thus brought to consider that world-wide source of terrestrial deformation—earthquakes; but I should forget the indulgence of your patience up to this point, if I should now undertake any partial review of these astonishing and alarming occurrences. I am deeply impressed, however, with an aspect of the subject that demands attention, that throws into sharp relief the prophecies of disaster, with which, willingly or unwillingly, we have all become familiar.”
The lecturer here rolled forward to the front of the platform, a blackboard on which in colored chalks the earth, looking somewhat like a shortened egg, with its north and south poles situated on the long, flattened sides, was depicted; while a black line or axis drawn through it terminated in the Sahara Desert on one side, and near the Society Islands on the other. Two ominous circles in vermillion were described on it, concentric respectively with the ends of the black line, one sweeping along the western coast of North and South America, and crossing the Isthmus of Panama, the other encircling the coasts of Africa and gathering in their fatal course the Azores, Canaries, and the Cape Verde Islands. And on both these terrifying curves, in black letters, was printed the hypnotic intimation “Belt of Weakness or Earthquake Ring.” The effect on the audience was sufficiently impressive. The staring rude drawing around which a cyclone of blue scratches, purporting to be clouds, was expressively raging, intensely steeped the observers in a spell of wonder and trepidation. Even Leacraft, by the contagion of a common obsession, craned his neck, and fixed his eyes with a stupid absorption upon the crazy and paradoxical diagram.
The speaker continued, noticing with undisguised satisfaction the ocular concentration produced by his obnoxious figure, with its anomalous portents: “It is well known that we have in the boundaries, or shore lines of the Pacific, a surprisingly larger number of earthquakes recorded, than anywhere else in the world, and this seems in some way coincident with the prevalence of active volcanoes in the same region. Prof. Haughton has enumerated for the world 407 volcanoes, 225 of which are active. Of these latter, 172 are on the margin of the Pacific. Prof. Milne, who lived a long time in Japan, for the express purpose of studying the earthquake problem of those islands, has observed the surprising frequency of their earthquakes, and it is a volcanic zone they occupy. We have in contradistinction to this area about the Pacific a reversed circle which envelopes the western coast of Africa, and by this chart,” here the lecturer pushed back the blackboard, and, standing alongside of it, began, with a pointer of elucidation, a direct allocution to that subject of confusion, “we are made immediately cognizant of the opposite and yet symmetrical disposition of these zones. This should have from its simplicity and a quasi-permanency, in its phenomena—its earthquake phenomena—a general explanation. The explanation is not reassuring; it is not proven, but it is accepted by many, and has, for me, a very reasonable probability. Let us at least not recoil from its consideration.”
Under the encouragement of this exhortation, the audience seemed to slide forward in their seats a few inches, with the impetus of a renewed hope.