486 TRANSACTIONS OF SECTION C. 
area, but is somewhat more persistent as a definite band in the southern and 
eastern portions of the district. The true relation of these horizons to each 
other is seen in the type section at Gelli Grin, where the Bala Limestone 
at its maximum thickness is overlain by light-coloured, pasty mudstones 
containing a typical Rhiwlas Limestone fauna. The fauna is not nearly so rich 
in individuals as that of the Rhiwlas Limestone itself, but all the more 
important genera and species seem to be represented. Confirmatory sections are 
also seen east of the fault near Gelli Grin farm, and also on Bryn Cut. 
3. Plant Petrifactions in Chert and their bearing on the Origin of Fresh- 
water Cherts. By Manin C. Storgs, D.Sc., Ph.D. 
The author described, and illustrated with photos, petrifactions of plants in 
the fresh-water cherts of Lulworth (Purbeck) and Asia Minor (Tertiary). The 
author drew special attention to the Asia Minor cherts, which are remarkably 
interesting and contain well-preserved plant debris. These were described by 
Mr. Haydon in his Presidential Address to the Liverpool Biological Society, but 
his work seems not to have reached most geologists and paleobotanists. The 
cherts contain beautifully preserved pollen grains, fungi, stem debris, &c.; 
and the existence of these delicate soft tissues so well preserved suggests that 
Sollas’ view of flint formation can only be applied with caution to these fresh- 
water cherts. 
The author drew attention to the recent ‘Sapropel’ observed by Potonié, 
and the likeness it has to the debris in the Asia Minor chert; concluding that 
the chert may be taken as practically pure petrified ‘Sapropel,’ a phenomenon 
which must interest those who are concerned with the methods of plant 
petrifactions. 
4. Critical Sections of the Cambrian Area called The Cwms in the 
Caradoc-Comley Region of Shropshire. By KH. 8. Cosson, F.G.S. 
The work of excavation of critical sections in the Cambrian rocks of Shrop- 
shire has been continued by the writer at intervals during the past year, and 
has furnished palzontological proofs of the prolongation of the Lower and 
Middle Cambrian rocks of Comley into the Cwms area to the south. The 
sections opened up confirm and amplify those excavated in previous years. 
Excavation No. 53 supplies details of the upper portion of the Wrekin 
Quartzite and the lowest part of the Lower Comley Sandstone, near the base 
of which three fossiliferous bands are found, yielding species provisionally 
referred to Kutorgina, Hyolithus, Hyolithellus, and Archcocyathus. 
Excavation No. 54 exhibits a section of the junction of the Middle and 
Lower Cambrian beds, which is very closely comparable with those of the 
Quarry Ridge at Comley. 
The beds in descending order are as follows :— 
e. Shale with Grit Bands=The Quarry Ridge Shale, top not seen 4 feet 
d. Hard, ringing, glauconitic Grit=The Quarry Ridge Grit . : lial 
c. Conglomerate=The Quarry Ridge Grit, conglomeratic portion re 
b. Dark Grey, Purplish and Red Limestones=The Black, Grey, 
and Olenellus Limestones of Comley . ; 2 P . about 4 ,, 
a. Green, Micaceous Sandstones, with Spotted Bands=The Lower 
10a. 
The conglomerate ¢ is plentifully charged with fragments of the Black and 
other Lower Cambrian Limestones, and it is now proved for the first time that 
the Black Limestone must be grouped with the Lower Cambrian. 
The surface of the solid Black Limestone is coated with a phosphatic (?) skin, 
and a similar deposit in the Comley Quarry has within the last two or three 
years yielded recognisable fragments of Paradoxides sp. and Dorypyge Lakei 
Cobbold. The black skin must, therefore, be regarded as the lowest deposit of 
the Middle Cambrian age that is known in the district. 
Comley Sandstone; base not seen 
