3810 Bernard Smith—Upper Keuper, East Nottinghamshire. 
cohered mud from tranquil waters. The passage from sandy shales 
to fine marls mentioned above rather favours the first of these 
alternatives. In addition we must not forget that wind-borne dust 
and sand would also add largely to the fine sediment. The rate of 
deposit in muddy rocks may be as much as 9-18 inches per hour 
according to Sorby, the shaly character of the coarser parts being due 
to a gentle current of varying velocity carrying sediment of various 
degrees of fineness. 
We may, then, sum up the formation of skerry-belts as follows :— 
(a) Rather shallow waters slowly becoming desiccated during a dry 
period; deposition of fine sediment as marl, some possibly wind- 
borne and distributed by water, for under favourable conditions 
even the blocky marls show signs of bedding and current-action. 
Formation of salt crystals in the upper clayey layers. 
(6) Influx of fresh water bringing sediment. Casts taken of salt 
crystals, now dissolved out. Formation of skerry by successive 
freshets of water and current-action. 
(c) As supply of coarse sediment failed, laminated shales were 
deposited, finally passing into fine sediment as marl. Conditions 
repeated for every skerry. 
On this idea, other things being equal, every individual sherry 
represents a wet spell of greater or less duration or degree. A skerry- 
belt might therefore represent a sequence of wet seasons, and we 
have an explanation of the persistence of the skerry-belts and general 
types of sediment over large areas whilst the individual skerries are 
of less extent. 
Colour Changes.—A discussion of the variegated colours of the 
Keuper is beyond the limits of this paper; one or two remarks, 
however, may not be out of place. We cannot assume that all the 
red beds were once green, or that all the green beds were once red. 
There have been changes about tree-roots and along joints where 
red marl has become green, but the deciding factor for the big colour 
changes must have been one connected with the mineral solutions 
in the water and their concentration. In this connexion the above- 
mentioned gradual change in colour with each skerry when well 
developed is suggestive. With the influx of fresh waters the 
conditions which previously brought about a red colour were upset, 
and a green took its place, followed by alternating red and green 
conditions until the red finally prevailed as the waters became more 
concentrated. 
Goodchild? has pointed out that the presence of organic and 
humic acids prevents the deposition of iron as ferric oxide—and 
most of the fossiliferous beds in the Keuper are grey or green. It 
does not therefore seem too great an assumption to suggest that 
the first torrential? waters sweeping down from the land not only 
cooled and diluted the previous solutions, but also carried with them 
organic remains and humic and organic acids which would for a time 
1 <¢ Desert Conditions in Britain’’: Trans. Geol. Soc. Glasgow, 1898, vol. xi, pt. 1, - 
pp. 87, 89, 90. 
2 Especially if humid conditions prevailed in the upper parts of the inland basin 
as in the case of the Dead Sea and the Great Salt Lake. 
