482 SECTIONAL TRANSACTIONS.—C, 
visible, but the eastern one shows a junction with a quartzite conglomerate. 
The length of the visible portion of the dike is just under 400 yards, while 
the greatest breadth is 125 yards. ‘The crinanite occurs as medium-grained 
and very coarse varieties which have sharp, unchilled junctions, and segre- 
gation veins are abundant: ‘These veins include felspathic, zeolitic, and 
picritic types. ‘The last type occurs as a contemporaneous marginal modi- 
fication, and thus affords an interesting problem in differentiation. The 
mutual relations of the various modifications are discussed in this paper. 
AFTERNOON. 
Excursion to Corby ironstone district. Leaders: Prof. W. G. 
FEARNSIDES, F.R.S., Dr. A. F. HALLIMOND. 
Tuesday, September 12. 
Discussion on The origin of red sedimentary rocks (10.0) :-— 
Prof. G. HICKLING. 
There has long been almost universal agreement that ‘ red rocks’ are of 
non-marine origin; but the exact conditions under which they have been 
formed are still open to discussion. "They show two marked facies : un- 
stratified sandstones, and red marls of peculiar composition which often 
contain saline deposits. Normal limestones are absent, but magnesian lime- 
stones may be developed. Breccias and conglomerates of several unusual 
types are commonly found. Fossils are rare and occur sporadically in very 
restricted areas. Except in the occasional magnesian limestones, which 
may yield stunted marine forms, the fossils are restricted to fishes, land 
vertebrates and a limited flora. Long duration of stable conditions is 
indicated by the occurrence of faunas of widely different ages in a sandstone 
mass without any determinable stratigraphical break between them. ‘The 
red coloration is attributable to prolonged exposure of the sediments above 
the ground-water level, though they may have been subsequently distributed 
and deposited by water. It is aided by the total absence of carbonaceous 
colouring matter which results from a restricted flora and the complete 
oxidation of any organic remains. Red rocks may show a lateral passage 
to a marine facies, usually with an intermediate zone of alternating conditions. 
It is suggested that the rocks are the product of arid or semi-arid delta or 
flood-plain conditions, and that the explanation of the different types of 
deposit is to be sought mainly in variations of humidity and temperature, 
coupled with the effect of earth-movement in bringing the surface of deposi- 
tion above or below the level of the ground-water. 
Prof. W. S. BouLTON. 
Arising from his studies of the Red Rocks of the Midlands, the speaker 
refers to breccia- and conglomerate-formation in relation to contem- 
poraneous earth movement. Attention is drawn to peculiarities of recurrent 
coloration in sands, and to peculiarities in Spirorbis limestones. I 
Prof. W. T. Gorpon. 
The evidence of the plants as to the physical and climatic conditions 
during the formation of the red beds. 
