400 _ Dr. Du Riche Preller—Contact-Zone of 
the brickfield in the Ampthill Clay, but with that I cannot agree. 
The lowest beds normally exposed in the brickfield belong to a zone 
which has always been counted in England as part of the Kimmeridge 
Clay—the zone we have been accustomed to call alternans zone, but 
which Dr. Salfeld has told us is wrongly so called (provisionally 
I would call it the serratum zone). Sixteen years ago I saw deeper 
beds of clay exposed at the brickfield (in the foundations for the 
chimney-stack), but I did not recognize any of the beds in the 
railway cutting as identical with these. ‘here must therefore be 
some thickness of clay outcropping in the 700 yards between the two 
exposures, and this may include the representative of Dr. Salfeld’s 
warte zone." 
The mapping of zones along the outcrop of a thick mass of clay is 
not an easy matter through an inland area, mainly grass-land, but it 
may be of some practical value. The clays of different zones are not 
of equal value tor brickmaking, or at least not equally suitable for 
particular processes; and in the selection of a site for new works 
some means of determining which type of clay will be found at 
a suitable depth must be desirable. Such a means may be found in 
a zonal map. 
IlI.—THe Contact-Zonr oF THE ALPS AND THE APENNINES IN 
Western Liguria. 
By C.S. Du RicHE PRELLER, M.A., Ph.D., M.I.H.E., F.G.S., F.R.S.E. 
I. Iyrropucrory. 
N a paper on the Permian formation in the Maritime Alps, etc. 
(Guot. Mac., 1916, pp. 7-17), I mentioned incidentally that 
it extends from those Alps, viz. from the Montgioie range east into 
Liguria as far as the Savona Hills. As in the former so also in the 
latter region, that formation is composed of essentially gneissic schists 
known as apenninites or besimaudites belonging to the Lower Permian 
or Permo-Carboniferous, and of sericitic schists, quartzites, and 
clastic rocks or ‘ anagenites’ which constitute the Upper Permian or 
Verrucano proper, forming a transition to the Lower Trias.” The 
geological limit of the Permian in the Savona Hills coincides more or 
less with the geographical line of division of the Alps and Apennines 
at the Colle or saddle—also called Bocchetta—d’Altare; but another 
geological line of division exists still further east, at the junction — 
of the Triassic and Eocene formations in the Chiaravagna Valley near 
Sestri Ponente, immediately west of Genoa. In reality the geological 
division is marked, not by either of those lines but by a contact-zone 
between them. This contact-zone occupies the whole of Western 
Liguria and comprises two distinct and dissimilar parts: one, the 
Triassic cale-schists and pietre verdi area or Voltri group, which 
extends for about 25 kilometres along the Riviera littoral west of 
Genoa from Sestri Ponente to Voltri, Varazze, and Celle Ligure, 
INQ? -Gist, xix, p. 42371913. 
2 This division has its exact equivalents in the Apuan Alps or Carrara 
Mountains as the lowest formation underlying the marmiferous Trias, and in 
the Verrucano—a name derived from Monte Verruca—of the Pisan Hills. 
