The effect of finite electrical and thermal conductivities on magnetic buoyancy in a rotating gas

A horizontal magnetic field if increasing in strength downwards can cause a horizontal layer of electrically conducting fluid to become unstable, a phenomenon known as ‘magnetic buoyancy’, and sometimes thought to have relevance to magnetic A stars, and to sunspot creation. Analyses that assume infinite thermal and electrical conductivities (and zero viscosity) predict that modes of zero horizontal wave-length, in the direction perpendidular to the field, are maximally unstable but are stabilised by even small Coriolis forces. It is shown here, however, that when proper allowance is made for the finite (though large) conductivities of the fluid the layer may experience a ‘conductive instability’ that grows on the ohmic time-scale and is maximally unstable to a mode of non-zero horizontal extent.     

The structure of the Moine and Dalradian Rocks in the Dalmally District of Argyllshire,Scotland

Two phases of deformation are described from the area. D1 is related to the first phase movements widely recognised in the Dalradian; D2 is related to more localised modifications of the D1 fold pattern. Four major D2 folds are recognised from the evidence of minor structures. Three of these, the Beinn Chuirn, the Ben Lui and the Ra Chreag Folds, had previously been considered as D1 structures, whilst the fourth, the Dalmally Fold, was unrecognised. These folds provide continuity between the southeast facing of the D1 folds of the Moine and Ballachulish Succession of Glen Orchy (Thomas and Treagus 1968) and the southeast facing of the D1 Jay Nappe (Shacketon 1958) in the Iltay Succession above. The D2 deformation reaches a climax at the junction between the two Successions, the Iltay Boundary Slide, which is now regarded as a D2 structure. The regional implications of these results are briefly considered.     

Post-survey Likert constructions: an adaptive method for generalizing perceptions of environmental variability

GeoJournal - Environmental perceptions are inherently based on an individual’s existing knowledge, experiences, and future expectations. Methods for measuring environmental perception,...     

A Unified Approach to Mean Field Electrodynamics

Using the first order smoothing approximation and a novel technique (double Fourier transformation and expansion) a number of results, new and old, in the theory of mean field electrodynamics and magnetohydrodynamics are given a systematic and general derivation. They are cast into forms which bring into new prominence the role of the helicity spectrum in induction processes. The situations in which the results may be expected to be accurate are delineated. New expressions are given for the reduction in the mean electromotive force created by the LORENTZ forces acting on the microscale turbulence.     

Jointing and minor tectonics of the S. Crop of the South Wales Coalfield between Machen and Bridgend

Observations on joints, minor faults and mineral veins at 47 localities along the south and south east crop of the S. Wales Coalfield indicate the presence of a joint system comprised of up to 6 sets of fractures striking at 350°, 330°, 290°, 270°, 250° and 210°. The joint sets are parallel to minor faults of strike and dip-slip types, whilst minor thrust faults indicate an early phase of sub-horizontal compression. The joint system is thought to be of tectonic origin and developed early in the deformational history of the area in response to a N-S compression. Later, dilational episodes facilitated the infilling of mineral veins, with the W.N.W. trending set probably indicating the latest phase of dilation in the area. All structures are considered to be of Armorican age, whilst the marked similarity in the orientation of the joint system to that of the North Crop of the Coalfield suggests that the brittle deformation was relatively homogeneous on both flanks of the Coalfield.     

Succession and structure in the Llwyd Mawr Syncline,Caernarvonshire north Wales

A succession of strata ranging in age from Upper Cambrian to Valentian is described. They occupy ground in, and adjacent to, the Llwyd Mawr syncline. Most of the rocks are marine but during mid-Caradocian (Soudleyan) times a rhyolitic ignimbrite sheet was emplaced and rests disconformably on Llanvirn slates. It has a remanant thickness of 2300 ft and is a single cooling unit. A second volcanic episode (Lower Longvillian) produced 600 ft of bedded pyroclastic rocks with only subordinate ignimbrites. Mid-Caradocian minor intrusions of rhyolite occur as domes and sills in association with the volcanic rocks. Minor intrusions of dolerite and micro-tonalite are probably of Caledonian age. Three phases of movement are recognized within the main end-Silurian Caledonian movements. The first movement phase, F1, produced the main fold architecture and the dominant associated axial-planar cleavage, S1. The folds, which possess a Caledonoid trend, usually stand vertically, but rarely they verge slightly to the southeast. They are periclinal in style. The second movement phase, F2, was weak and produced a sporadically distributed set of open folds and associated axial-planar crenulation cleavage, S2, of Caledonoid strike. The axial-planes dip gently to the southeast quadrant. Folds of the third movement phase, F3, plunge northwest and the associated axial-planar crenulation cleavage, S3, dips steeply to the northeast. The F3 folds produce a pronounced arcuation in the trace of the Fl structures from an azimuth of 60° in the northwest to 10° in the south of the area.     

Jointing and minor tectonics of the N. Crop of the South Wales coalfield between kidwelly and black mountain,S. Wales

Joints, minor faults and mineral veins were recorded at 334 stations between Kidwelly and Black Mountain, S. Wales. A systematic pattern occurs with joint sets striking at 360°, 340°, 290°, 250°, and 210°. Minor faults and shear planes exhibit both strike and dip-slip displacements. The jointing is considered to have formed quite early during folding, and both joints and faults can be attributed to a principal compression acting almost N-S and subparallel to bedding. Phases of dilation are recorded by sets of mineral veins. All the deformational structures are considered to be of Armorican age.