ART. 2. PETROLOGY AT GOOSE CEEEK SHANNON. 3 



of Goose Creok quarry, has been published by Roberts.^ In this paper 

 this mass of intrusive diabase is named the Belmont Stock. 



GENERAL DESCRIPTION. 



The quarry exposes no contacts of the intrusive -rocks with the 

 nclosing sediments. The material exposed consists in greatest part 

 of the igneous rock, described below as normal diabase. Next irs 

 abundance comes a rock which does not differ greatly in composition 

 from the normal diabase but which is very coarse grained, the mate- 

 rial of the maximum coarseness containing augite blades 25 cm. (10 

 inches) in length and 3 cm. in width. A third type comprises other 

 masses, usually of small size, with a similar coarse texture but con- 

 sisting in the main of albite and quartz, the titaniferous augite which 

 is characteristic of the first two types being more or less completely 

 replaced by diopside. This type is considered to be in part an enid 

 differentiate of the coarse second type and in part a hydrothermal 

 alteration product. The masses of the third type contain small 

 miarolitic cavities lined with contemporary crystals of quartz, albite, 

 titanite, and diopside, usually also with a later series of minerals con- 

 sisting of fine fibrous hornblende, epidote, chalcopyrite, and chlorite. 

 The fourth rock type consists also mainly of quartz and albite, and 

 occurs in narrow dikes of aplitic habit filling persistent narrow cracks 

 in the normal rock. These dikes are considered to be essentially of 

 the same origin as the magmatic third rock type, the principal dif- 

 ference being the textural change caused by their intrusion into 

 narrow cracks. 



All of the rock types considered are cut by numerous joints and fis- 

 sures. Adjacent to these there is hydrothermal alteration of the 

 inclosing rocks of various types which are discussed below^, and the 

 cracks and open spaces themselves are filled with minerals deposited 

 from solution. These minerals, which are described individually in 

 detail in the following pages, consist of several varieties each of horn- 

 blende and chlorite ; epidote, albite; the sulphides, galena, chalcopyrite, 

 pyrite, and possibly pyrrhotite; diopside, axinite, datohte, prehnite' 

 apophyllite, quartz, calcite, laumontite, chabazite, stilbite, etc. There 

 appears to be represented in the limits of the quarry a gradation 

 from the original crystallization of the normal diabase through a 

 series of magmatic differentiates into high temperature hydrothermal 

 deposits, represented by the hornblende in cracks and the minerals 

 in the miarolitic cavities. The latter overlap a sequence found in 

 the veins which grades into the series of minerals characteristic of 

 typical zeohtic deposits. 



2 Joseph K. Roberts, Jurassic Intrusives of Virginia. Pan-American Geologist, vol. 39, pp. 289-296 May 

 1923. . -t't' . J-, 



