Suchergebnisse

La cuprosklodovskite est triclinique ; ses paramètres sont :
a = 7.04 À, b = 9.18 Â, c = 6.66 Â, a = 109°14', ß = 90°0', y = 108°22'.
Les cristaux, aciculaires, sont allongés suivant l'axe a [100] et portent les faces
{001}, {011}, {010}, {111}, {110}, {120}, {210}.
Les macles sont fréquentes, soit avec axe de macie [100] et plan de jonction (010), soit avec plan de macie (210).
L'orientation optique est précisée, ainsi que les indices de réfraction et l'angle des axes optiques.

La jachimovite appartient au système triclinique, groupe spatial Pl. Ses paramètres, déterminés par Mélon et Dejace, sont a = 7,04 Å, b = 9,18 Å, c = 6,66 Å, ɑ = 109°14', β = 90°00' et γ = 108°22'. Z = 1[CuH2(UO2SiO4)2 . 5H2O].
La méthode d'investigation était la diffraction des RX par un monocristal. L'interprétation de la fonction de Patterson, suivie de synthèses de Fourier normales et des différences, montre que le minéral présente une structure en feuillets parallèles, constitués par les ions (UO2SiO4)[formula] unis entre eux par les cations Cu++.

The author has considered three quadratic forms (i) ƒ = Gaβduaduβ (ii) θ = μaβduaduβ and (iii) Φ — ξaβduaduβ. With the help of these quadratic forms ten distinct families of ruled surfaces have been obtained. The intersection of these ruled surfaces with the surface of reference yields interesting results. Also, some particular cases have been studied.

The author shows that the thermodynamics of the plane capillary layer described with the aid of a Gibbs dividing surface may not allways be applied to any dividing surface. The use of an arbitrary dividing surface is correct only when the chemical potentials satisfy to two conditions. These two conditions are satisfied in the case of equilibrium, but out of equilibrium, the use of an arbitrary dividing surface involves a loss of generality.

The equations for the evolution in time of irreversible processes are written in a variational form in some important cases (thermal conductibility, chemical reactions). The stationnary non equilibrium states are shown to be characterized by a minimum of a quadratic function of the velocities or rates of the irreversible processes. In the neighbourhood of equilibrium, this function reduces to the entropy production per unit time in accordance with a theorem derived previously by the author. The variational principle introduced here which may be called «the principle of the least velocities », plays a role somewhat similar to the Gauss principle of the «least constraints » in classical mechanics.

In the type-region of the Maastrichtian of Dumont for a long time strata have been recorded which differ considerably in faune from the underlying Maastrichtian tuffaceous chalk.
Recently they were again discovered in the neighbourhood of Geul-hem (6 kms NE of Maastricht) and, on account of the microforami-nifera they yielded, ascribed to the Paleocene by Hofker.
The definition of the age of these layers offers an important strati-graphical problem : the fixation of the upper limit of the Maastrichtian and its relations with the Secondary-Tertiary boundary, which problem occupies many micropaleontologists and stratigraphers in the world at present.
In 4 localities layers were observed differing from the underlying tuffaceous chalk in lithological aspect by the presence of a more or less large quantity of glauconite. They are separated from the latter by a typical hard ground or by a series of coarse strata rich in fossils conspicuously reworked from the Maastrichtian.
The hard ground contains many Ammonites, Baculites and other typical cretaceous Molluscs and the underlying tufïaceous chalk, characterized by abundant Hemiaster prunella, yielded several Belem-nella Casimir ovensis, which is generally considered as the last Belem-nite of the Maastrichtian.
The overlying glauconitic tuffaceous chalk did not yield any Ammo¬ nite or Belemnite, but a macrofauna composed of species which do generally not occur in the Maastrichtian. Crania brattenburgica, a characteristic Brachiopod of the Danian of Denmark, is represented here by the subspecies Cr. brattenburgica geulhemensis.
Examination of the planktonic Foraminifera from samples taken at several levels and spots in the various sites showed a marked change in microfaune above the hard ground or its equivalent. In the tuffa-ceous chalk planktonic Foraminifera, though relatively rare, were found forming an association of typical cretaceous species, with the exception, however, of a representative of the group Girt, compressa, species until now known from Post-Maastrichtian deposits only. In the glauconitic tuffaceous chalk the planktonic fraction consists of an entirely different association, with dominating species Gl. daub-jergensis, which species characterizes Danian strata all over the world.
The author concludes that the upper limit of the Maastrichtian in the type-region is characterized by a typical hard ground or its lateral equivalents. The overling strata are, especially on account of the planktonic Foraminifera they contain, ascribed to the Danian.