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The microgranite grades southwards into feldsparphyric rhyolite with feldspar phenocrysts up to 40 nun long. Asimilar relationship also occurs in a dyke trending 085°, which is exposed (2213 1190) on the southwest'coast.Numerous, narrow, feldsparphyric rhyolite dykes, separated by screens of medium-grained granite as narrow as 2m, are well exposed on the coastline (209 129) south of the jetty. The dykes mostly trend eastnortheast, anddominate the outcrop.Barren Hills. In the Barren Hills, south of Silver Mine Bay, feldsparphyric rhyolite dykes (Plate 28) are dominantand intrude the medium-grained Lantau Granite. They trend eastnortheast On the coast (1838 1222) between NgauKwu Wan and Shui Tseng Wan, the dykes contain large granite xenoliths, up to 1.5 by 8 m across.Siu Kau Yi Chau. Almost the entire island is composed of feldsparphyric rhyolite and porphyritic microgranitedykes, which locally grade from one to the other. On the south coast (2405 1654), a flow-banded feldsparphyricrhyolite dyke trends 065°, and cuts another feldsparphyric rhyolite dyke. To the east, there are rapid texturalchanges to microgranite, with abundant small phenocrysts, rarely up to 20 mm long, and then back tofeldsparphyric rhyolite, whose texture is dominated by large feldspar phenocrysts set in an aphanitic groundmass.Peng Chan. On Tai Lei, a small island northwest of Peng Chau, good exposures (2155 1680) of feldsparphyricrhyolite grade, over a width of 2 m, into porphyritic microgranite, but within 5 m the rock texture reverts tofeldsparphyric rhyolite. A narrow chilled margin, trending 080°, is developed along the contact with an adjacentdyke.A feldsparphyric rhyolite dyke, trending approximately eastwards, cuts fine-grained granite east of Tung Wan. Thedyke, which is up to 20 m wide, can be traced for 300 m. On the east coast (2278 1642), it has aphyric,flow-banded margins to both north and south, whereas its central zone varies from feldsparphyric rhyolite toporphyritic microgranite. Similar relationships occur elsewhere along the east coast of Peng Chau.Discovery Bay. Feldsparphyric rhyolites dykes, which intrude medium-grained granite, and porphyriticmicrogranite dykes, are exposed at numerous localities along the coast around Discovery Bay. Complex, compositeintrusive relationships occur between the feldsparphyric rhyolites., with or without small feldspar phenocrysts, andporphyritic microgranites in cut slopes (1948 1646) east of the golf course. The groundmass in the feldsparphyricrhyolites varies locally from aphanitic to microcrystalline.Between Sam Pak Wan and Sz Pak Wan, north of Discovery Bay, there are good examples of dykes which gradefrom feldsparphyric rhyolite to porphyritic microgranite. Their margins tend to be coarsely porphyritic, whereas thecentres have fewer, smaller phenocrysts.Siu Ho Wan. Along the coast west of Siu Ho Wan , there are several good exposures of younger feldsparphyricrhyolite dykes chilled against older dykes. In addition, textural gradations occur between light grey feldsparphyricrhyolite, with phenocrysts of feldspar up to 20 mm long, and porphyritic microgranite, with a fine-grainedgroundmass and phenocrysts of less than 10 mm.Yam O Wan. A feldsparphyric rhyolite dyke (2036 2181) on the island of Cheung Sok, north of Yam 0 Wan,contains phenocrysts which are progressively smaller towards the south. It becomes a porphyritic microgranite withabundant quartz and feldspar phenocrysts up to 2 mm across. The northern margin of the dyke, which intrudes tuffof the Shek Lung Rung Member, is flow banded, and contains feldspar crystals up to 20 mm long.Complex relationships between feldsparphyric rhyolite and poiphyritic microgranite occur on the eastern shores ofYam O Wan (209 213). Gradational contacts between the two occur across both wide (several metres) and narrowzones. In addition, multiple dyke contacts are well exposed.Tung Chung Wan. On the west side of the bay, a feldsparphyric rhyolite dyke, with aphanitic margins and aporphyritic microgranite centre, trends 055°, and intrudes fine-grained granite to the north (1038 1625).Tsing Yi. Rhyolite dykes, crowded with feldspar megacrysts, are very common on Tsing Yi They range from a fewmetres, up to 200 m wide, and extend for up to 1 km. In the north, around Chung Mei (2830 2350), a number ofdykes, up to 40 m wide and trending generally eastaortheastwards, intrude tuff, granodiorite and granites. Rhyolitedykes clearly intrude megacrystic, fine-grained granite southwest of Chung Mei (2827 2327), and also tuff to itssouth (2842 2336), and granodiorite to its east (2844 2347). Further east, near Ko Tai (2905 2345), and southeastat Cheung Ching (2921 2300), feldsparphyric rhyolite intrudes medium-grained granite.In the southern part of Tsing Yi the rhyolite dykes are generally rich in feldspar megacrysts. They are wider andmore extensive than to the north, and trend easterly. A major group of dykes, the largest over 200 m wide, intrudestuffs and is exposed in road cuts (2785 2216 and 2759 2191) south of Nam Wan. In one outcrop (2777 2205), therhyolite is intruded by thin dykes of fine-grained granite. This group of dykes can be traced eastwards to the main( 81 (