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Lin Fa Shan. The steep eastern flanks of Lin Fa Shan are composed of alternating rhyolite lava flows and beds oftuffaceous sandstone, or siltstone. The sedimentary rocks form cliffs, most of which are inaccessible. However, onthe west side of the hill, extensive exposures of the highest beds include massive, or poorly bedded, tuffaceoussandstone and scarce, finely laminated mudstone. Sandstone and siltstone beds, 200 m west of the summit (14821420), dip to the north at 34°, and graded units indicate they are the right way up. West of the summit, the bedsgenerally dip steeply to the east or northeast, and may form part of a syncline whose axial plane trace trendsnorthwards along the ridge. The ridge is capped in places by lapilli-ash tuff of the Sunset Peak Member, but theirstratigraphic relationship to underlying strata is uncertain.Sedimentary EnvironmentThe restricted geometry of the sedimentary rocks, and the rapid gradational changes, suggeststhat they accumulated in small basins filled during flash floods, and by debris flow mechanisms.During more quiescent periods, silts were deposited. The pronounced grading in many of thesiltstones, best seen on a microscopic scale, may have resulted -from seasonal changes, orlocalized rainstorms on the flanks of a poorly consolidated volcanic pile. The large tuffaceousunits have some mass flow characteristics, and the volcano on which these basins developedprobably degraded rapidly between pyroclastic and extrusive phases. The flora, containingbennettitaleans and ferns suggest a warm, wet palaeoclimate (Zhou Z.Y., Nanjing Institute ofGeology and Palaeontology, written communication, 28 May 1992).Palaeontological and Other Age ConstraintsDuring the present survey, fossil plants have been found at five localities within the LantauFormation; Man Cheung Po, Lung Tsai Ng Yuen, Sham Hang Lek, Shek Lam Chau and SunsetPeak. Fossils have also been found by Lee et al (1990), and Nau & Wu (1991) near NgongPing. Macrofossil preservation at Sham Hang Lek and Shek Lam Chau is relatively poor, as isthe preservation of all miospores.Davis (1952) recorded dark bluish-grey mudstone with fossil leaf specimens in outcrops east ofSunset Peak: These fossils were tentatively identified as Equisetites, Pterophyllum, andPodozanites lanceolatus, and the outcrop was thought to be part of the Jurassic HsiaopingSeries found northwest of Guangzhou. Edwards (in Lee et al. 1990) stated that these fossilsranged from Middle Jurassic to Early Cretaceous. Lee et al. (1990) examined fossil plantscollected from Ngong Ping and Lung Tsai Ng Yuen, and concluded that the strata probablycorrelate with the Gaojiping Formation of Guangdong, although they preferred an EarlyCretaeous age for the flora, as opposed to the conventionally accepted Middle to Late Jurassicage of the Gaojiping Formation. They did not, however, distinguish their flora with respect to thedifferent geographical areas of Hong Kong, and it should be noted that only one of the plants(Scleropteris tibeticd) used for age determination is present on Lantau Island.Nau & Wu (1991) looked at flora from Ngong Ping and Lung Tsai Ng Yuen on Lantau Island,as well as from Cheung Sheung in the east of the New Territories. They concluded that theLantau specimens are older than the Upper Jurassic Cheung Sheung rocks, and could be lateEarly to early Middle Jurassic, emphasising in particular the presence of Coniopteris burejensis,Ptilophyllum pecten and Otozamites graphicus as indicators of this age.Nanjing Institute of Geology and Palaeontology have reappraised (Appendix 3) the plant fossilscollected on Lantau Island by P. S. Nau (Hong Kong University), and specimens collected duringthe present survey, and conclude that only two fossils, Otozamites yizhangensis Zhang andIThinnfeldia sinensis Zhang, are of stratigraphic significance. Zhou Z.Y, (Nanjing Institute,written communication, 28 May 1992) stated that Otozamites yizhangensis was originallydescribed from the basal Liassic (Hettangian to Sinemurian) strata of southern Hunan(Kindianmen Formation), and that Thinnfeldia sinensis has also been found in southern Hunan.Zhou concluded that this plant assemblage is of early Early Jurassic age.53