230 The A III erica u Geolocjist. April, 1895 
first definition of tiu' i)i-ini()r(lial zone; simply defined the ''Par- 
udoxides l)eds," wliieli have since l)een Tound tol)e in the Mid- 
dle Cambrian. Plainly the bottom of tiie Cambrian was not 
seen by him. In Wales Middle and L'ppei- ( 'amV>rian faunas 
have been developed l»y Salter and Hicks, antl l>y others, but 
no paleontologic base line has been found. Even the Olenellus 
zone has not there been discovered. This being the birth-place 
of the term, to which its later-discovered extensions must be 
referred for verification, the query might arise whether on pal- 
eontologic grounds the strata carrying Olenellus really belong- 
to the ( -amln-ian. However, the Olenellus strata have later 
been detected in Shropshire, bordering on Wales, ajid may 
reasonably be expected to extend into Wales. In northwest- 
ern Scotland also these strata are well developed. ]»ut seem tO' 
be succeeded directl}^ l)y the upper (Olenus) beds, though no 
transgressive non-conformity between the Olenellus strata and' 
the Olenus beds has been definitely esta])lished. The base of 
the Cambrian here presents a curious complexity. It is in- 
volved in a series of faults and thrust-fractures. The lowest 
rock which lies on the Archean unconformably is the Torridon 
quartzyte, as yet not proved to be fossiliferous, and non-con- 
formably al)ove it are found strata carrying the Olenellus 
fauna. The Torridonian quartzyte is from 8,000 to 10,000 
feet thick. It had been included in the (Cambrian,* notwith- 
standing the con-conformity at its summit, until the fucoid 
bed above the non-conformit}' was found to contain Olenellus,. 
when it was immediately referred to the Pre-Cambrian. The 
profound non-conformity at the base of the Torridon quartz- 
yte has a wide extension, and its significance has been re- 
marked on by several English geologists. As a datum from 
which to begin the reckoning of Paleozoic time it holds 
first rank, and there ought to be some better reasons for 
excluding it from the Cambrian than the non-discovery of 
characteristic Cambrian fauna. In the Longmynd region, also,, 
similar irregularities occui-, but at this place the strata are 
broken by volcanic and other igneous interpositions. Some- 
have claimed that even the Longmynd strata are Pre-Cam- 
brian, i. e. Archean, because, apparently, Olenellus occurs 
above them, with evidence of volcanic disturbance between^. 
*A. GEIKIK. (,)ii;irl. .Iniir. ( ;.•()!. Soc, Aii.i;., ISSS, p. 400. 
