The Precarboniferous Rocks of Charnwood Forest.—Part II

Abstract

The Microscopic Structure of the Charnwood Rocks. In many cases the task of determining the nature and structure of these rocks is comparatively easy; but in others it presents great difficulties. These arise from the amount of metamorphism which the rocks have undergone since they were first deposited. This metamorphism may be said to be of a double nature :—the one, readily apprehended by the eye, that which has converted sandstone into quartzite, and fine felspathic detritus into something resembling a felspathic igneous rock, being in all probability the combined effect of pressure, heat, and water; the other, almost wholly revealed by the microscope, in which the last of the above-named agents of change has probably been the most active, and which may still be in progress—namely, the gradual decomposition of the minerals which once composed the rocks, and the formation of new ones by fresh combinations of the chemical elements thus set free. This process often obscures, far more than the former, the original structure of the rock; and it is this accordingly which causes our main difficulty in the study of these Charnwood rocks. To investigate microscopically all the varieties of stratified rocks found in the Forest would be a most laborious task; and in all probability the result would not compensate for the labour. We have therefore selected a series of specimens which appeared either typical of the more important varieties, or likely to be useful in illustrating some point of structure or stratigraphy. Forty-four slides in

Palaeomagnetism of Late Precambrian or Cambrian diorites from Leicestershire, U.K.

“…1). At Enderby the diorites intrude slates probably of Precambrian to Cambrian age (Hill & Bonney, 1878;Cribb, 1975); elsewhere the intrusive relationships of the diorities below the Triassic cover are not apparent. Rb-Sr whole rock ages of 546 + 22 Ma and 552 ±58 Ma (2a) from the diorites of south Leicestershire (Enderby-Croft region, Fig.…”

Description and crystal structure of bobkingite, a new mineral from New Cliffe Hill Quarry, Stanton-under-Bardon, Leicestershire, UK

“…Both quarries work a diorite (Snowball, 1952) from one of a series of dioritic laccoliths, the South Charnwood diorites, near the junction of the Maplewell and Brand members of the (Precambrian) Charnian Series of pyroclastic and epiclastic rocks (Sylvester-Bradley and Ford, 1968). The South Charnwood diorites crop out in an arc between Brodgate Park and Stantonunder-Bardon, and probably form part of a single intrusion (Hill and Bonney, 1978;Worrsam and Old, 1988). The diorite consists of primary calcic amphibole, calcic plagioclase and quartz that has altered to epidote, carbonate white mica and chlorite.…”

Paleobiologia de Cloudina sp. (Ediacarano, Grupo Corumbá): implicações tafonômicas, taxonômicas e paleoecológicas

“…Os primeiros trabalhos que citam fósseis atualmente reconhecidos como representantes da Biota Ediacarana remontam ao século XIX (Ramsay, 1858;Billings, 1872;Hill & Bonney, 1877). Porém, nesta época, o consenso científico considerava esses estratos cambrianos, visão que perdurou até os clássicos trabalhos de Sprigg (1947Sprigg ( , 1949, no qual são descritos, pela primeira vez, fósseis de corpo mole das colinas de Ediacara, na Austrália.…”