The minerals of picrites are very frequently decomposed. Serpentine partly or wholly replaces olivine, forming radiate fibrous masses which are green, yellow or red in microscopic sections. Sometimes hornblende (pilite), talc, chlorite and mica appear as secondary products after olivine. The augite passes into chlorite or into green fibrous or platy amphibole. Hornblende and biotite are often fresh when the other components are much altered. The felspar is rarely in good preservation but yields epidote, prehnite, sericite, kaolin; calcite and analcite are abundant in some Weathered picrites.
Rocks of this type are well represented in Great Britain. In the central valley of Scotland several masses of picrite have been discovered, always in closing association with olivine-diabase and teschenite. One of these forms the island of Inchcolm in the Firth of Forth, another lies near Bathgate (in Linlithgowshire), and there are others at Aberdour (Fife), Ardrossan and Barnton (Midlothian). They belong to the (great series of Carboniferous eruptive rocks of the Scottish midland valley. These picrites are not known to be represented in England, but, on the other hand, there are Devonian picrites in Devon and Cornwall as basic members of the diabase and proterobase series of these counties. Some of them contain much augite like the picrite (often called palaeopicrite as being of palaeozolc age) at Menheniot Station in Cornwall and the picrite of Highweek near Newton Abbot in Devonshire. Others are hornblende-picrites like that of Cartuther near St Germans, Cornwall. Hornblende-picrite occurs also in the island of Sark and several beautiful examples have been described from Anglesey and from Penarfynnydd in North Wales and from Wicklow in Ireland. picrites occur in several parts of Germany, notably in the Devonian rocks of the Fichtelgebirge and Nassau, where they accompany diabases and proterobases l1ke those of Cornwall and Devonshire. In Silesla and Moravia picrites are found with teschenites like those of Central Scotland in some of the continental picrites enstatite is present but is rare. In North America picrites occur among the igneous rocks on the Hudson river and in Alabama and Montana. (J. S. F.)
PICROTOXIN, a neutral principle obtained from the Cocculus
indicus, which is the fruit of the Anamirta paniculata. It is
used in medicine externally as an antiparasite. Internally it
has been successfully used to check the night sweats of phthisis.
In large doses it is a powerful poison, causing unconsciousness,
delirium, convulsions, gastro-enteritis and stimulation of the
respiratory centre followed by paralysis, from which death
sometimes results. Formerly low class publicans sometimes
added Cocculus indicus berries to beer to increase the intoxicating
effects. Its chemical formula is C15H16O6•H2O.
PICTET DE LA RIVE, FRANÇOIS JULES (1809–1872), Swiss zoologist and palaeontologist, was born in Geneva on the 27th of September 1809. He graduated B. ès. Sc. at Geneva in 1829, and pursued his studies for a short time at Paris, where under the influence of Cuvier, de Blainville and others, he worked at natural history and comparative anatomy. On his return to Geneva in 1830 he assisted A. P. de Candolle by giving demonstrations in comparative anatomy. Five years later, when de Candolle retired, Pictet was appointed professor of zoology and comparative anatomy. In 1846 his duties were restricted to certain branches of zoology, including geology and palaeontology, and these he continued to teach until 1859, when he retired to devote his energies to the museum of natural history and to special palaeontological work. He was rector of the academy from 1847 to 1850, and again from 1866 to 1868. He was for many years a member of the Representative Council of Geneva, and in 1862 President of the Constituent Assembly. His earlier published work related chiefly to entomology, and included Recherches pour servir à l’histoire et à l’anatomie des Phryganides (1834) and two parts of Histoire naturelle, générale et particulière des insectes Neuroptères (1842–1845). Feeling the want of a hand-book, he prepared his Traité élémentaire de paléontologie (4 vols. 1844–1846). In the first edition Pictet, while adopting the hypothesis of successive creations of species, admitted that some may have originated through the modification of pre-existing forms. In his second edition (1853–1857) he enters further into the probable transformation of some species, and discusses the independence of certain faunas, which did not appear to have originated from the types which locally preceded them. He now directed his attention to the fossils of his native country, more especially to those of the Cretaceous and Jurassic strata, and in 1854 he commenced the publication of his great work, Matériaux pour la paléontologie suisse, a series of quarto memoirs, of which six were published (1854–1873). In this work Pictet was aided by E Renevier, G. Campiche, P. de Loriol and others. Pictet also brought out Mélanges paléontologiques (1863–1868). He died at Geneva on the 15th of March 1872.
Obituary by W. S. Dallas, Quart. Journ. Geol. Soc. (1873), vol. xxix.
PICTON, SIR THOMAS (1758–1815), British general, was the
younger son of Thomas Picton, of Poyston, Pembrokeshire,
where he was born in August 1758. In 1771 he obtained an
ensign’s commission in the 12th regiment of foot, but he did
not join until two years afterwards. The regiment was then
stationed at Gibraltar, where he remained until he was made
captain in the 75th in January 1778, when he returned to
England. The regiment was disbanded five years later. On
the occasion of its disbandment Picton quelled a mutiny amongst
the men by his prompt personal action and courage, and was
promised a majority in reward for his conduct. This, however,
he did not receive, and after living in retirement on his father’s
estate for nearly twelve years, he went out to the West Indies
in 1794 on the strength of a slight acquaintance with Sir John
Vaughan, the commander-in-chief, who made him his aide-de-camp
and gave him a captaincy in the 17th foot. Shortly
afterwards he was promoted major. Under Sir Ralph Abercromby,
who succeeded Vaughan in 1795, he took part in the
capture of St Lucia (for which he was promoted lieutenant-colonel)
and in that of St Vincent. After the reduction of
Trinidad Abercromby made him governor of the island. He
administered the island with such success that the inhabitants
petitioned against the retro cession of the island to Spain, and
their protest, with Picton’s and Abercromby’s representations,
ensured the retention of Trinidad as a British possession. In
October 1801 he was gazetted brigadier-general. But by this
time the rigour of his government, as reported by his enemies,
had led to a demand by humanitarians at home for his removal.
Colonel William Fullarton (1754–1808) procured the appointment
of a commission to govern the island, of which he himself was
the senior member, Captain (afterwards Admiral Sir Samuel)
Hood the second, and Picton himself the junior. Picton thereupon
tendered his resignation, and Hood, as soon as the nature
of Fullarton’s proceedings became obvious, followed his example
(1803). On his way home Picton took part with great credit
in military operations in St Lucia and Tobago. Realizing,
however, that the attacks upon him were increasing in virulence,
he quickly returned to England, and in December 1803 he was
arrested by order of the privy council. He was tried in the
court of king’s bench before Lord Ellenborough in 1806 on a
charge of unlawfully applying torture to extort a confession
from Luise Calderon, a mulatto woman of loose character who
was charged, along with a man, with robbery. The torture
consisted in compelling the woman to stand on one leg on a flat-headed
peg for one hour. The punishment was ordered under
Spanish law (which in default of a fresh code Picton had been
appointed to administer in 1801) by the local alcalde, and
approved by Picton. On these grounds the court returned a
merely technical verdict of guilty, which was superseded in
1808 by a special verdict on retrial. It should be mentioned
that the inhabitants of the island, who had already given him
a sword of honour, and had petitioned the king not to accept
his resignation, subscribed £4000 towards his legal expenses,
which sum Picton contributed in return to the relief of the
suffering caused by a widespread fire in Port of Spain. He had
meanwhile been promoted major-general, and in 1809 he had
been governor of Flushing during the Walcheren expedition.
In 1810, at Wellington’s request, he was appointed to command
a division in Spain. For the remaining years of the Peninsular
War, Picton was one of Wellington’s principal subordinates.
The commander-in-chief, it is true, never reposed in him the
confidence that he gave to Beresford, Hill and Craufurd. But
in the resolute, thorough and punctual execution of a well defined
task Picton had no superior in the army. His début,
