Vol. 56.] THE SOTTTH-EA.STEKN COAST OF JERSEY. 317 



The presence of micropegmatite is common in the altered rocka 

 from St. Elizabeth's Castle and near Fort Eegent, as Prof, de 

 Lapparent has pointed out. 1 He clearly recognizes that the 

 intimate penetration of the ' epidiorite ' (diabase) by the acid 

 magma has resulted in the absorption of material by the intruder, 

 and that we have produced ' une roche mixte, a, la fois verte et 

 rosee, ou le quartz pegmatoi'de court comme une trame au milieu 

 des elements encore reconnaissables de Fepidiorite.' The process 

 of alteration in the diabase so closely resembles other instances 

 from Jersey that a detailed description would be mere repetition. 

 There is the same gradual increase in the size and number of the 

 acid patches, and it is interesting to note the gradual isolation 

 in those of the felspars of the diabase. They frequently become 

 coated over with a layer of acid felspar, or of this and quartz in 

 more or less micropegmatitic contact. The possible occurrence 

 of allanite in one or two slides is of interest. This mineral has 

 been recorded from these rocks by Prof, de Lapparent. 2 



The field-evidence is completely in accord with the microscopic. 

 A gradual change can be traced from the red unadulterated granite, 

 poor in the dark minerals, to a reddish-yellow rock rich in both 

 hornblende and mica, and crowded with the dark felspars of the 

 diabase. Here and there occurs a less completely disintegrated 

 fragment. Often such dark fragments are scattered in a canary- 

 yellow rock speckled plentifully with the dark minerals. As the 

 latter increase in quantity it becomes gradually more difficult to 

 distinguish the fragments, until the rock appears to be neither 

 ' diorite ' nor granite. This may be explained by the absorption 

 and impregnation of the diabase in various degrees by an acid 

 magma. The phenomena of Havre des Pas are essentially similar. 

 The boundary of the red and dark rocks could be traced sometimes, 

 but at others the blur of colour round the junction was very 

 marked. 



A slide cut from a dark dioritic rock below Port Eegent is worthy 

 of brief mention. It was presumably once a diabase, but a thin- 

 section shows it to contain a considerable quantity of quartz and some 

 pale acid felspars, usually added zonally to the opaque lath-shaped 

 felspars of the older rock. No augite is found, but green hornblende 

 is frequent in a granular form, recalling the glomeruli mentioned 

 in a former paper. 3 Irregular flakes of a rather fibrous brown 

 mica and flakes of magnetite are associated with the hornblende- 

 grains. Frequently the latter are not more than *012 inch in dia- 

 meter, and instead of being closely packed together are dispersed, 

 favouring the acid felspar in their distribution. The colourless 

 acicular crystals referred to sillimanite are not uncommon. 



The intrusive aplite of St. Elizabeth's Castle and of the shore 

 under Fort Eegent is in all probability the same as the aplitic 



1 'Les Roches eruptives de l'lle de Jersey/ Ann. Soc. Sci. Brux. vol. xvi. 

 t. ii (1892) p. 233 [sep. cops. p. 14]. 



2 Ann. Soc. Sci. Brux. vol. xvi, pt. ii (1892) p. 234 [sep. cops. p. 15]. 



3 Quart. Journ. Geol. Soc. vol. lv (1899) p. 441 and reference given there. 

 Q.J.G.S. No. 222. z 



