422 Notices of Memoirs—LIron-ores of Wales. 
and Middle Coal-measures), like the Leicestershire and South Derby- 
shire Coalfield, of which it is a continuation ; and none of the Red 
series (or Transition series and Upper Coal-measures) of the North 
Staffordshire type are met with in this area west of a line somewhat 
east of the Nottinghamshire and Derbyshire County boundary between 
Bolsover and Stanton, though this line probably curves westward in 
the north, just south of Rotherham, and eastwards, south and south- 
east of Nottingham. 
A summary of the fossil flora and fauna of North Derbyshire and 
Nottinghamshire, as at present known, was given, with the horizon 
and locality of the specimens cited. This, though preliminary, was 
in extension of the work already accomplished in the Leicestershire 
and South Derbyshire Coalfield, shortly to be published, and in other 
fields, and supplementary to the work of Ward, Hind, and Stobbs in 
the North Staffordshire Coalfield on the mollusca and fish fauna of 
that area, and of Kidston on the fossil floras of Yorkshire and North 
and South Staffordshire. 
VI.—On rue Pisorrrrc Iron-ores or Wates. By W. G. Frarnsrpss, 
M.A., F.G.S. 
HE first part of the paper discusses the occurrence of the well- 
known iron-ores of Caernarvon and Merioneth, and shows that 
though they have been taken by various writers as marking a well- 
constituted subdivision of the Tremadoc slates they are really of the 
nature of fissure phenomena, and may occur at almost any horizon. 
The various worked exposures seem always to agree in the following 
particulars :— 
(1) They are associated with the occurrence of large hypabyssal or 
minor plutonic intrusions of sill-like habit, and occur among stratified 
rocks along the limit of the sill’s metamorphic area. 
(2) They occur in more or less lenticular masses, of no considerable 
lateral extent, often heaped together and separated by crushed shale 
partings in a way which may suggest bedding, but often thinning out 
yet maintaining a linear arrangement across considerable tracts of 
country. 
(3) Considerable lenticles of ore are always associated with dark- 
blue or black shales or slates, which nearer to the igneous intrusion 
have become bleached and spotted through the influence of that 
intrusion. On the side of the ore body nearest the intrusion the 
country rock is usually little disturbed, and lies evenly, but on the 
side remote from the intrusion the country rock is crossed and recrossed 
by planes of slickenslide, and is often intensely nodular. 
The more important stratigraphical horizons which have developed 
pisolitic ore bodies in the North Welsh district are :— 
(1) Lower Lingula flags. Bettws Garmon. Black shales which 
underlie the grey flaggy sandstones with Lingulella beds. 
(2) Upper Lingula flags. North flank of Aron Mawddy. Adjoining 
shales contain Peltwra scarabaoides. 
(3) Upper Arenig Shales. Moelwyn Bach; Milltirgerig, Arenig ; 
below Llyn y gader, Cader Iris. Country rock contains 
abundant Didymograptus bifidus. 
