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 P A C P A C 129 ances in the Maldive group of atolls without any necessity for disseverment by oceanic currents as argued by Darwin. Precisely the same explanation is applied to the case of a barrier reef. It commences in the shallow water near the shore, and afterwards extends seawards on a talus built up of lumps of coral broken off by the surf. A very careful examination of the barrier reef at Tahiti was made by Lieutenant Swire of H.M.S. &quot;Challenger&quot; and Mr Murray, and they found that such an explanation was completely justified by the form and nature of the reef. There was much dead coral on the inner side of the barrier, which in many places was perpendicular or even overhanging; while, on the contrary, the outer surface was all alive, and sloped gradually sea wards. * A section of it, drawn to a true scale, is given in fig. 10. FIG. 10.- Section across the Barrier Reef, Tahiti. This section shows that a ledge, over which there is a depth of from 30 to 40 fathoms of water, runs out for 250 yards from the edge of the reef. This ledge is covered with luxuriant heads and bosses of coral. Beyond it there is a steep irregular slope at an angle of about 45, the talus being formed apparently of coral masses broken off from the ledge, and piled up ; this slope is covered with living Sponges, Alcyonarians, Hydroids, Polyzoa, Foraminifcra, and other forms of life. The angle of inclination then decreases to 30, and the ground is covered with coral sand ; while beyond 500 yards from the edge of the reef the declivity is insignificant, only 6, and there is a bed of mud containing volcanic and coral sand mixed with Pteropod and other shells, in 590 fathoms of water. The vast perpendicular wall of coral limestone descending into unfathomable depths, which has been supposed usually to mark the outside of a coral reef, has always been looked upon as a conclusive proof of great subsidence having taken place ; but the depth and the slope of such limestone walls have been greatly exaggerated, and no means have been taken to ascertain beyond doubt that the rock is formed of coral throughout. The probability is that only the upper portion of such a wall is true coral limestone; and Dr Guppy has recently shown that this is actually the case in some upraised coral islands of the Solomon group. Upheaval has taken place to a considerable extent in the oceanic islands, and more extended examination of the limestone cliffs of other coral islands will probably lead to the discovery of many such cases. Mr Murray holds that the characteristic form of barrier reefs and atolls is in no way dependent on subsidence, that subsidence is not the cause of their peculiar features, that these reefs may be met with indifferently in stationary areas, in areas of subsidence, and in areas of elevation, and that elevation and sub sidence only modify in a minor way the appearance of the islands. The chief phenomena are accounted for (1) by a physiological fact, the very vigorous growth of the reef-forming species on the outer or seaward face of the reef where there is abundance of food, and the much less vigorous growth, and even death, of these species on the inner parts of the reefs and in the lagoons, where there is much less food, and where there are other conditions inimical to growth; and (2) by a physical and chemical fact, the removal of lime in suspension and in solution from the inner portions of the reefs and from the lagoons, where much dead coral is exposed to the action of sea iater containing carbonic acid, the result being the formation, the deepening, and the widening of lagoons and lagoon channels. For further information on subjects referred to in this article see John Murray, &quot; On the Structure and Origin of Coral Reefs and Islands,&quot; Proc. Roy. Soc. Edin., vol. x. p, 505; Alex. Agassiz, &quot;On the Tortugas and Florida Reefs,&quot; Tranf. Amer. Acad., vol. xi. (1883); Archd. Geilue, -The Origin of Coral Reefs,&quot; Nature, vol. xxix. pp. 107 and 124; John Murray and A. Renard, &quot;On the Nomenclature, Origin, and Distribution of Deep-Sea Deposits,&quot; Proc. Roy. Soc. Edin,, vol. xii. p. 495 (1884); John Murray and A. Renard, &quot;On the Microscopic Characters of Volcanic Ashes and Cosmic Dust, and their Distribution in the Deep-Sea Deposits,&quot; Proc. Roy. Soc. Edin., vol. xii. p. 474, 1884. (J. MU.) PACUVIUS, MARCUS (219-129 B.C.), was the second in order of time of the three tragic poets who wrote for the Roman stage in the 2d century B.C. His life was so long that he might be described as a contemporary of all the writers who flourished during the first period of Roman literature. He was born in 219 B.C., when Livius Andronicus and Naavius were introducing their imitations of the Greek tragic and comic drama to Roman audiences ; he was recognized as the chief tragic poet about the time when Caecilius, and after him Terence, were the nourishing authors of Latin comedy ; he continued to produce his tragedies till the advent of the younger poet Accius, who lived on till the youth of Cicero ; and he died in the year (129 B.C.) when Lucilius first appeared as an author. He stood in the relation of nephew as well as pupil to Ennius, by whom Roman tragedy was first raised to a position of influence and dignity. In the interval between the death of Ennius (169) and the advent of Accius, the youngest and most productive of the tragic poets, he alone maintained the continuity of the serious drama, and perpetuated the character first imparted to it by Ennius. Like Ennius he probably belonged to the Oscan stock, and was born at Brundisium, which had become a Roman colony in 244 B.C. To this origin may be attributed the fact that he never attained to that perfect idiomatic purity of style which was the special glory of the early writers of comedy, Najvius and Plautus. 1 The fame of his uncle Ennius may probably have drawn him to Rome, and may have induced him to devote himself to the composition of tragedy. But he obtained distinction also as a painter ; and the elder Pliny mentions a work of his which in his time was still to be 1 ^Etatis illius ista fuit laus tanquam innocentiae sic Latine loquendi ; nee omnium tamen ; nani illorum aequales Csecilium et Pacuvium male locutos videmus ; sed omnes turn fere, qui nee extra urbem hanc vixerant nee eos aliqua barbaries domestica infuscaverat, recte loque- bantur (Cicero, Brutus, 74). seen in the temple of Hercules in the forum boarium. His relationship to the friend of the great Scipio would naturally recommend him to the consideration of the eminent men of the next generation, who fostered the new literature in his spirit ; and thus Cicero, in the De Amicitia, represents C. Lselius as speaking of him as &quot;hospitis et amici mei.&quot; He was less productive as a poet than either Ennius or Accius and we hear of only about twelve of his plays, founded on Greek subjects (among them the Antiope, Teticer, Armorum Judicium, Dulorestes, Chryses, Niptra, &c., most of them on subjects connected with the Trojan cycle), and one &quot; Praetexta,&quot; Paulus, written in connexion with the triumph of L. jEmilius Paulus, for his victory at Pydna, celebrated in the year 167 B.C., as the Clastldium of Nsevius and the Ambrada of Ennius were written in commemoration of great military successes in their time. He continued to write tragedies till the age of eighty, when he exhibited a play in the same year as Accius, who was then thirty years of age. He retired to Tarentum for the last years of his life, and a story is told by Gellius of his being visited there by Accius on his way to Asia, who read to him one of his plays, which was famous in after times, the Atreiis. The story is probably, like that of the visit of the young Terence to the veteran Caecilius, due to the invention of later grammarians ; but it is invented in accordance with the traditionary criticism of the distinction between the two poets, the older being characterized rather by cultivated accomplishment, the younger by vigour and animation. &quot; Ambigitur quoties uter utro sit prior, aufert Pacuvius docti famam senis, Accius alti. &quot; 2 He died at the age of ninety, having lived through the long period from the beginning of the Second Punic War xvin. 17
 * Horace, E., ii. 1, 54, 55.