562 C0. Johns—Classification of the Lower Carboniferous Rocks. : 
and aluminium present and to the gradual conversion of soluble 
colloidal forms of alumina, of iron peroxide, of silicate, and possibly 
of certain silicates with insoluble modifications during the exposure 
of the rocks to the atmosphere. The deposition of the hydrated 
oxides of iron from the dissociation of naturally produced solutions of 
carbonate of iron is doubtless in many places also a factor in the 
induration of the laterite in situ. 
WEATHERING AND Decomposition oF Rock anp Soits In THE TROPICS. 
In his investigations on weathering of rocks in the Tropics, Mr. E. C. J. Mohr 
(Bul. Dept. Agr. Indes Neerland, No. 32, pp. 26, figs. 2, 1909) records the effect of 
rain-water on freshly ground Tertiary basalt under moist warm climatic conditions 
as follows :— 
The rock was used in three sizes, + to 4, 1 to 14, and 3 to 4mm. particles. It 
was subjected to the action of rain-water from July, 1906, to December, 1908, in 
an apparatus so arranged that in one series the level of the water was above that of 
the rock particles, and in the other the particles were kept moist by rise of water 
from below. ‘The principal fact noted in the first series was that the silicic acid 
corresponding to the decomposed augite and lime felspar was washed out with the 
soluble bases, while the silicic acid corresponding to the alkali felspar remained 
behind as kaolin. In the second series, only the silicic acid corresponding to 
decomposed augite was removed, and the silicic acid corresponding to lime felspar 
remained behind. (Experiment Station Record, vol. xxii, No. 8.) 
Note. Owing to a copyist’s error, the figures 8°26, against ‘‘ Iron Protoxide’’, 
incorrectly appear in the analysis of the ‘l'umatumari Laterite (in Table IV on 
p. 446 of the October number of the Gon. Magc.), and should be deleted, the 
summation of the analysis being carried out as 100-45, the correct figures. 
VI.—On tHe Crassirication oF THE Lower Carponirerous Rocks. 
By Cosmo Jonns, M.I.Mech.E., F.G.S. 
N this communication it is proposed to briefly note the divisions 
which have been proposed for the Lower Carboniferous Rocks of 
Great Britain and Belgium; to discuss their validity in the light of 
the important additions that have been made to our knowledge during 
the last few years; and to suggest a new classification which, while 
expressing the physical and faunal changes which characterized that 
particular time interval, shall be generally applicable and at the same 
time do justice to the workers who have contributed most largely to 
our knowledge. 
It will be necessary to clearly define what is meant by the Lower 
Carboniferous. In Staffordshire, Derbyshire, and North-West Yorkshire 
the line has been drawn at the base of the Ingleborough or Kinderscout 
Grit or its equivalent. In Scotland the Roslin Sandstone is the 
dividing line, and in the first and last of the areas mentioned 
Mr. Kidston! has determined the great break between the Upper and 
Lower Carboniferous lloras to take place at this level. In Derbyshire 
and North-West Yorkshire a marked change of conditions occurs at 
the same level, and the Geological Survey in both places drew the 
line at the base of the massive Grit. By definition, therefore, Lower 
Carboniferous extends up to the level where the plant break occurs. 
No one has suggested extending the limits any higher, and to draw 
the line at a lower level would divorce the Upper Yoredale limestones 
with their rich coral and Brachiopod fauna from the lower limestones 
1 See Mem, Geol. Surv. Derby. and Notts. Coal-field, 1908, p. 9. 
