Annual report of the United States Geological Survey to the Secretary of the Interior . d the original bed-ding,where it can be often determined, coincides roughly with I lie planesof schistosity developed later. However, a careful study of the areawould probably show minor discordances abundantly. The hornblendeschists are chiefly altered augitic tuffs, but considerable sneaks of thetalc schists were without doubt formed from basic massive igneousrocks of the peridotite group, in which pyroxene is a prominentconstituent. A very interesting phenomenon of structure is shown in fig. 1!». Theschi
Annual report of the United States Geological Survey to the Secretary of the Interior . d the original bed-ding,where it can be often determined, coincides roughly with I lie planesof schistosity developed later. However, a careful study of the areawould probably show minor discordances abundantly. The hornblendeschists are chiefly altered augitic tuffs, but considerable sneaks of thetalc schists were without doubt formed from basic massive igneousrocks of the peridotite group, in which pyroxene is a prominentconstituent. A very interesting phenomenon of structure is shown in fig. 1!». Theschistosity represented by the broken lines is nearly everywhere paral-lel to the granite contact. In this respect the region represents astriking similarity to the Rainy Lake district described by LawsonJand which is particularly well brought out on the geological map thataccompanies his monograph. 1 Bull. Cool. Soc. Amn ion, Vol. II, pp. 49-74. * Auriferous Gravels, i>. 401. * Idem, * Tin geology of tin- Kiiiny Lake region : Ann. Kept. Cool. Survey. 1SS7. Pnrt TURNER] SCHISTOSITY AND BEDDING. 555 Professor Lawson writes (p. 142): An important discovery lias lieen made in the mapping of the relative distribu-tion of the upper and lower Archean, whereby it appears that the latter, consistingof Laurentian gneiss and granite, occurs in large isolated central areas more or lesscompletely surrounded by the schists of the upper Archean (now called Algonkian),the encircling belts anastomosing and forming a continuous meshwork. W i ii fJ/t//:
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