摘要:

AbstractOrdovician sediments at Tagoat and Rosslare Harbour are re‐described and their relationship to the underlying Rosslare Series discussed. A brief outline of their petrology is given, but it is shown that the fauna is in need of revision before reliable correlations can be made. Similar rocks are recorded near Tomhaggard; amongst these, spotted mudstones imply Ordovician or later intrusions. Undeformec dykes intrusive into the Rosslare Series are believed to be representatives of this phas

ISSN:0072-1050    

DOI:10.1002/gj.3350050102

出版商:John Wiley&Sons Ltd    

年代:1966

数据来源: WILEY

ISSN:0072-1050    

DOI:10.1002/gj.3350050103

出版商:John Wiley&Sons Ltd    

年代:1966

数据来源: WILEY

摘要:

AbstractThe preservation of molluscan shells as calcite casts is commonly a result of their centripetal replacement, while on the sea floor, by a stable micrite envelope. This grows in three stages: (1) algae bore into the shell wall, (2) the algal filaments die and decay, (3) micritic aragonite fills the tubes. Later, if the skeletal sand is exposed to fresh water as a result of uplift or a fall in sea level, or to a suitable brine deep under the sea floor, the residual molluscan shell is dissolved but the envelope remains intact. It forms an empty mould that is subsequently filled with drusy calcite. Complete replacement of skeletal grains by micritic aragonite yields cryptocrystalline grains like Ming's “grains of aragonite matrix” and the grains in Beales's “bahamite”. Through a study of compaction fabrics it may be possible to decide whether an envelope‐bearing limestone was cemented above sea level or below the

ISSN:0072-1050    

DOI:10.1002/gj.3350050104

出版商:John Wiley&Sons Ltd    

年代:1966

数据来源: WILEY

摘要:

AbstractA new classification of concretions is suggested. Some concretions are described from the Upper Cambrian (Maentwrog) sediments of St. Tudwal's Peninsula, southwest Caernarvonshire, and their age relative to that of the surrounding sediments is discussed.

ISSN:0072-1050    

DOI:10.1002/gj.3350050105

出版商:John Wiley&Sons Ltd    

年代:1966

数据来源: WILEY

摘要:

AbstractMagnetic anisotropy measurements have been made on fifty‐four oriented samples from the Carna and Screeb areas of the Galway Granite, and from the Ardara pluton and the Main Granite (including the Trawenagh Bay Granite) in Donegal. The origin of magnetic anisotropy in plutonic magnetic rocks is discussed, and it is concluded that it is probably due to grain alignment of inequant magnetite, which may occur either as free grains or as secondary inclusions in ferromagnesian minerals. The grain alignment may occur either whilst the magma is essentially fluid, giving a magnetic lineation transverse to the flow, or at a much later stage of consolidation during plastic deformation, in which case the magnetic lineation parallels the direction of greatest elongation.The results of the measurements are consistent with macroscopic foliations and lineations where these have been observed, but also indicate the existence of fabrics too weak to observe by conventional methods. This is because the magnetic method assesses the alignment of a very large number of grains, and is therefore much more sensitive than conventional fabric analysis. The weak fabrics can be qualitatively explained in terms consistent with other evidence relating to the emplacement of the granites, and experimental work now in progress may make possible a more quantitative interpretatio

ISSN:0072-1050    

DOI:10.1002/gj.3350050106

出版商:John Wiley&Sons Ltd    

年代:1966

数据来源: WILEY

摘要:

AbstractNearly ten years have elapsed since Korzhinskii proposed his basis of paragenetic analysis in 1957. During this period the method was developed and popularised by including diverse problems of physico‐chemical petrology and the study of mineralisation. In the process, definite progress has been made in solving theoretical and practical problems. The present review does not pretend to be a full discussion of research in this field: its aim is reassessment of the most important achievements in certain problems of metamorphism, granitic and syenitic magmatism, metasomatism and formation of ore

ISSN:0072-1050    

DOI:10.1002/gj.3350050107

出版商:John Wiley&Sons Ltd    

年代:1966

数据来源: WILEY

摘要:

AbstractThe survey is based on field work by Flinn, on forty‐two K‐Ar age determinations by Miller, and on previously published work on Shetland. Most of the metamorphic rocks give K‐Ar ages of about 420 m.y. It is clear from petrological and stratigraphical evidence that this age is not the age of the metamorphisms and migmatizations responsible for the more obvious features of the rocks, and also that the metamorphic rocks in different areas have had different histories of development. Ages up to 515 m.y. have been found in various areas, and these may be more closely related to the main metamorphisms than the more common 420 m.y. ages. In the Mainland the 420 m.y. age may be related to a late porphyroblast metamorphism: in Unst and Fetlar it seems to be the age of Read's second metamorphism which accompanied the emplacement of nappes and the formation of orogenic sediments. About 400 m.y. ago a series of postorogenic granitic and appinitic complexes were emplaced in the southern part of Shetland. By 380 m.y. ago erosion had reached migmatitic rocks and they were being buried again beneath Old Red sediments and contemporaneous volcanics. Later still, possibly 350 m.y. ago, in Upper Devonian times, granites were emplaced in the west of Shetland cutting the Old Red rocks. Finally the Walls Boundary Fault (Great Glen Fault ?) cut one of these late gra

ISSN:0072-1050    

DOI:10.1002/gj.3350050108

出版商:John Wiley&Sons Ltd    

年代:1966

数据来源: WILEY

摘要:

AbstractThe calcite‐quartz bodies which occur in the Upper Wenlock slaty succession of Llangollen have a distinctive fabric of platy calcite crystals and coarse, sometimes euhedral, quartz. The calcite internal deformation lamellae and folds and boudins formed in the bodies during the production of the folds and cleavage of the country rock are described together with the recrystallization fabrics of some of the calcite. Note is made of similar rocks from Ribblesdale and Coniston and their origin discusse

ISSN:0072-1050    

DOI:10.1002/gj.3350050109

出版商:John Wiley&Sons Ltd    

年代:1966

数据来源: WILEY

摘要:

AbstractThe high‐temperature and medium‐pressure part of the PT‐diagram of the system SiO2‐H2O has been investigated experimentally. The equilibrium diagram is discussed in the light of Schreinemakers general theory of PT‐diagrams.The triple invariant point cristobalite + tridymite + quartz lies at 1190°C and 1430 atm. Neither cristobalite nor tridymite are stable at high pressure. Quartz may precipitate from the melt at a very high temperature (1360°C and higher), if the pressure is great enough, and if the water content is low.Using new experimental and published data a PT‐diagram of the system SiO2‐H2O in the large PT

ISSN:0072-1050    

DOI:10.1002/gj.3350050110

出版商:John Wiley&Sons Ltd    

年代:1966

数据来源: WILEY

摘要:

AbstractThe highly fossiliferous fore‐reef limestones of B2age from near Castleton, Derbyshire are rich in Polyzoa. Ten species are described, six of them ne

ISSN:0072-1050    

DOI:10.1002/gj.3350050111

出版商:John Wiley&Sons Ltd    

年代:1966

数据来源: WILEY