Prof. S. H. Reynolds—The Rocks of the Avon Section. 545 
D. The Seminula Beds. 
S, continues the second Modiola phase of the Avon Section. 
S, (a).—Mainly calcite mudstones with algal, ostracodal, and 
Seminula layers and a Lithostrotion (Diphyphyllum) band at the 
base. Overlying these beds are limestones with Lithostrotion 
martin, and thick shaly partings. 
S, (b)—Mainly dark, massive, much dolomitized limestones, 
with abundant Lithostrotion martini, but including shaly partings 
and some bands of china-stone type. 
S, (a) The Seminula pisolite and associated rocks.—These consist 
of shallow-water deposits—calcite mudstones, dolomites, and 
pisolites associated with massive dolomitized Lithostrotion lime- 
stones. At the top are dolomites with three chert bands. 
These rocks form the upper part of the second Modiola phase of 
the Avon Section. 
S, (6) The Seminula Oolite——The lower part consists of massive 
white fossiliferous oolite, the grains being often formed round 
foraminifera. The upper beds, in addition to oolites, include 
foraminiferal limestones. 
S, (c).—The rocks of this level are chiefly massive foraminiferal 
limestones with Chonetes and Lxthostrotion bands, and are often 
considerably dolomitized. The upper beds include china-stones 
and pisolites and commence the third and last Modiola phase 
of the Avon Section. 
S, (d) The “ Concretionary Beds’’—These consist largely of 
china-stones with bands of Seminula pisolite and more rarely 
oolitic layers, but their most marked feature is afforded by the 
numerous “ Concretionary ”’ (algal) bands. 
KE. The Dibunophyllum Beds. 
D,.—The lower part consists of highly foraminiferal and coral- 
bearing white limestone associated with layers of coarse red oolite, 
and numerous bands of pseudobreccia. Thin shaly partings often 
separate the limestone bands. The upper part consists in the main 
of bands of coarse red oolite alternating with thick bands of shale 
and red grit. 
D,.—Except for the fact that this horizon commences with a 
band of quartz conglomerate, the lithological types are identical 
with those in D,- The lower beds are chiefly grey foraminiferal 
limestones and pseudobreccias, in the middle part coarse red oolites 
prevail, while the upper beds include much red grit and shale. 
II. Descriprion oF THE ROCKS FROM THE LiITHOLOGICAL 
ASPECT. 
(a) Calcareous Rocks. 
These may be classified according to the nature of their chief 
organic constituent :— 
VOL. LVIII.—NO. XII. 35 
