ordinary crystalline dolerite, which in a very short distance may
contain no vitreous base whatever. The spherulites may form the
greater part of the mass, they may be a quarter of an inch in diameter
and are occasionally much larger than this. These coarsely spherulitic
rocks pass over into the variolites (q.v.) by increasing coarseness
in the fibres of their spherulites, which soon become recognizable
as needles of felspar or feathery growths of augite. The ultimate
product of decomposition in this case also is a red palagonitic
substance, but owing to the absence of steam cavities the tachylyte
selvages of dikes are more often found in a fresh state than the
basic lapilli in ash-beds. Many occurrences of basaltic pitchstones
have been reported from Skye, Mull, and the western part of Scotland;
they are found also in connexion with the intrusive dolerite
sills of the north of England and the centre of Scotland. In the
Saar district of Germany similar rocks occur, some of which have
been described as weisselbergites (from Weisselberg).
Other localities for tachylytes of this group are Nassau, Silesia
and Sweden.
The chemical composition of some of the rocks of this group is
indicated by the analyses given below:—
|
SiO2 |
Al2O3 |
FeO |
Fe2O3 |
CaO |
MgO |
Na2O |
K2O |
H2O |
|
I. Palagonite. Seljadalr, Iceland......................
II. Palagonite from deep-sea deposits, Pacific
Ocean (with 2.89% MnO2)
III. Franz Joseph Land.....................................
IV. Tachylyte. Ardtun, Mull, Scotland................
V. Tachylyte. The Beal, Portree, Skye.............
|
|
|
38.96
44.73
35.48
53.03
52.59
|
|
|
11.62
16.28
8.30
20.09
17.33
|
|
|
|
14.75
14.57
12.30
9.53
11.14
|
|
|
|
|
|
|
17.85
9.56
16.80
2.64
3.27
|
|
(J. S. F.)
TACITUS, CORNELIUS (c. 55–120), Roman historian. Tacitus,
who ranks beyond dispute in the highest place among men
of letters of all ages, lived through the reigns of the emperors
Nero, Galba, Otho, Vitellius, Vespasian, Titus, Domitian,
Nerva and Trajan. All we know of his personal history is from
allusions to himself in his own works, and from eleven letters
addressed to him by his very intimate friend, the younger Pliny.
The exact year of his birth is a matter of inference, but it may
be approximately fixed near the close of the reign of Claudius.
Pliny indeed, though himself born in 61 or 62, speaks of Tacitus
and himself as being “much of an
age,”[1]
but he must have been
some years junior to his friend, who began, he tells us, his official
life under Vespasian,[2]
no doubt as quaestor, and presumably
tribune or aedile under Titus (80 or 81), at which time he must
have been twenty-five years of age at least. Of his family and
birthplace we know nothing certain; we can infer nothing
from his name Cornelius, which was then very widely extended;
but the fact of his early promotion seems to point to respectable
antecedents, and it may be that his father was one Cornelius
Tacitus, who had been a procurator in one of the divisions of
Gaul, to whom allusion is made by the elder Pliny in his Natural
History (vii. 76). But it is all matter of pure conjecture, as it
also is whether his “praenomen” was Publius or Gaius. The
most interesting facts about him to us are that he was an eminent
pleader at the Roman bar, that he was an eye-witness of the
“reign of terror” during the last three years of Domitian,
and that he was the son-in-law of Julius Agricola. This honourable
connexion, which testifies to his high moral character, may
very possibly have accelerated his promotion, which he
says[3]
was begun by Vespasian, augmented by Titus, and still further
advanced by Domitian, under whom we find him presiding as
praetor at the celebration of the secular games in 88, and a
member of one of the old priestly colleges, to which good family
was an almost indispensable passport. Next year, it seems, he
left Rome, and was absent till 93 on some provincial business,
and it is possible that in these four years he may have made
the acquaintance of Germany and its peoples. His father-in-law
died in the year of his return to Rome. In the concluding
passage of his Life of Agricola he tells us plainly that he witnessed
the judicial murders of many of Rome's best citizens from 93
to 96, and that being himself a senator he felt almost a guilty
complicity in them. With the emperor Nerva's accession his
life became bright and prosperous, and so it continued through
the reign of Nerva's successor, Trajan, he himself, in the opening
passage of his Agricola, describing this as a “singularly blessed
time,” but the hideous reign of terror had stamped itself
ineffaceably on his soul, and when he sat down to write his History
he could see little but the darkest side of imperialism. To
his friend the younger Pliny we are indebted for the little we
know about his later life. He was advanced to the consulship
in 97, in succession to a highly distinguished man, Verginius
Rufus, on whom he delivered in the senate a funeral eulogy.
In 99 he was associated with Pliny in the prosecution of a great
political offender, Marius Priscus, under whom the provincials
of Africa had suffered grievous wrongs. The prosecution was
successful, and both Tacitus and Pliny received a special vote
of thanks from the senate for their conduct of the case. It
would seem that Tacitus lived to the close of Trajan's reign, as
he seems[4]
to hint at that emperor's extension of the empire
by his successful Eastern campaigns from 115 to 117. Whether
he outlived Trajan is matter of conjecture. It is worth noticing
that the emperor Tacitus in the 3rd century claimed descent
from him, and directed that ten copies of his works should be
made every year and deposited in the public libraries. He also
had a tomb built to his memory, which was destroyed by order
of Pope Pius V. in the latter part of the 16th century.
Pliny, as we see clearly from several passages in his letters,
had the highest opinion of his friend's ability and worth. He
consults him about a school which he thinks of establishing at
Comum (Como), his birthplace, and asks him to look out for
suitable teachers and professors. And he pays[5]
him the high
compliment, “I know that your Histories will be immortal,
and this makes me the more anxious that my name should
appear in them.”
The following is a list of Tacitus's remaining works, arranged
in their probable chronological order, which may be approximately
inferred from internal evidence: — (1) the Dialogue on
Orators, about 76 or 77; (2) the Life of Agricola, 97 or 98;
(3) the Germany, 98, published probably in 99; (4) the Histories
(Historiae), completed probably by 115 or 116, the last years of
Trajan's reign (he must have been at work on them for many
years); (5) the Annals, his latest work probably, written in
part perhaps along with the Histories, and completed
subsequently to Trajan's reign, which he may very well have
outlived.
The Dialogue on Orators discusses, in the form of a conversation
which Tacitus professes to have heard (as a young man) between
some eminent men at the Roman bar, the causes of the decay of
eloquence under the empire. There are some interesting remarks
in it on the change for the worse that had taken place in the
education of Roman lads. The style of the Dialogue is far more
Ciceronian than that of Tacitus's later work, and critics have
attributed it to Quintilian; but its genuineness is now generally
accepted. It is noticeable that the mannerisms of Tacitus
appear to develop through his lifetime, and are most strongly
marked in his latest books, the Annals.
The Life of Agricola, short as it is, has always been considered
an admirable specimen of biography. The great man with all
his grace and dignity is brought vividly before us, and the sketch
we have of the history of our island under the Romans gives a
special interest to this little work.
The Germany, the full title of which is “Concerning the
geography, the manners and customs, and the tribes of Germany,” describes with many suggestive hints the general
- ↑
Pliny, Epp. vii. 20.
- ↑
Hist. i. 1.
- ↑
Ibid.
- ↑
Ann. ii. 61; iv. 4.
- ↑
Epp. vii. 33.
