Table 9. Mineralogical composition of Guyet Formation conglomerate. Rock Q 0 P Z B C C P 5 VR 3 M 0 no. T R L R 0 H H L L ee: T T T Z | G C 1g R 5 T T Seog! Y X H 1 2 1 37 4 17 g 23 7 2 g 1 1 5 17 ‘4 2 2 37 22 + C,MC 4 12 34 16 1 20 + 16 5 46 1 + + 14 8 20 13 6 55 + 1 36 1 2 1 2 2 1 7 4 2 69 11 6 6 4 8 16 84 1 M 9 8 + 71 6 5 3 3 4 10 24 2 + 25 13 10 27 11 57 1 15 x 6 12 5 10-1 3 + 42 13 18 11 3 1 oe 26-3D 67 + + 23 4 3 1 46-16 66 2 16 5 12 1 T 46-28 35 3 4 7 CRB 113-1 ad + + 1 33 2 + + 5 2 7 + T 113-1A 59 2 + 4 +5 3 1 6 3 7 Lt3-2 42 + 2 35 E 3 + 3 + 10 1 QM,M,T 126-25 43 1 + + + 19 5 7 6 4 8 7 1 QM,B 126-26 48 3 + 1 2 1 3 1 + TZ 23 1 QM,B Key QTZ = Quartz PLT = Pelite C = Chlorite ORT = Orthoclase SLT = Siltstone CRB = Carbonate PLG = Plagioclase VLC = Volcanic M = Muscovite ZRC = Zircon RXQ = Recrystalline quartz MC = Microcline BOP = Black opaques STY = Stylolites QM = Quartz mylonite CHR = Chert MTX = Matrix B = Biotite CHP = Cherty argillite OTH = Others + = less than 0.5 per cent All mineral percentages are rounded to the nearest integer Note: Samples 1 to 11 have been analyzed for strain and are discussed further in Appendix B. Reference areas for the Guyet Formation are at Mount Guyet and Summit and Alex Allen creeks. Thick- ness of the formation is variable because it is discontinu- ous. The formation is thickest where the conglomerate is predominant, as at Alex Allan Creek, Mount Guyet and Mount Tinsdale. In general the formation is from several metres to 400 m thick, commonly being between 100 to 300 m thick. It pinches out near Black Stuart Mountain. The lower contact of the Guyet Formation is con- formable onto parts of the black pelite unit of the Black Stuart Group and may be unconformable on the Waverly Formation north of Mount Guyet. Basalt clasts of the Guyet Formation conglomerate resemble basalt of the Waverly Formation and may have been derived from it. The sandy conglomerate (Fig. 19) underlies the area of Alex Allan Creek, Mount Guyet, and the island at the north end of Spectacle Lakes. Granule- to cobble-size clasts of green, tan, and grey chert to cherty argillite, grey to black chert, black pelite, light grey micaceous siltite and quartzite, and minor limestone and basalt are sup- ported in a sand-size matrix of quartz, chert, siltite and minor feldspar. The matrix clasts are subrounded to rounded. Granule to pebble chert fragments are angular to subrounded and siltite and quartzite are subrounded to rounded. Pebbles and cobbles of limestone are angular. Pelite and cherty argillite are in most places too deformed to estimate original shapes. The bedding within the sandy conglomerate is defined by layers of sand in which are supported coarse clasts and layers of sand with no coarse clasts. The sand matrix is continuous across the boundaries. Scoured contacts between overlying conglomerate and underlying sand- stone were seen locally but their frequency is unknown due to the type of exposure. The sandstone is planar bedded where bedding could be detected from trains of opaques. Channels of Guyet conglomerate are cut into the underlying black siltstone and pelite of the Black Stuart Group at the junction of Tinsdale and Cunning- ham creeks. The erosional relief is up to 75 cm and the width of the channels is on the order of 1 to 2 m. The sandy conglomerates of Alex Allan Creek and Mount Guyet are very similar in clast content, size, shape, percentage and distribution. The Spectacle Lakes occur- 29