546 Prof. S. H. Reynolds—The Rocks of the Avon Section. 
(1) Algal Limestones are abundant in all the rocks which 
accumulated under Modzola phase conditions, viz.: (a) in K, ; 
(b) at the top of the Caninia dolomite, C,; (c) m the lower part of 
S,; (d) in the Seminula pisolite bands of the lower part of 8, ; 
(e) in the Concretionary Beds of the upper part of 8,. Calcareous 
alge have also been met with in the lower part of C, and the middle 
part of §,. 
Mitcheldeania is the most persistent form ranging from the 
extreme base of the section to the top of 8,. Ortonella is 
characteristic of the K beds. Solenopora is found occasionally 
in the K beds. Spongiostroma associated with subordinate 
Mitcheldeania is prevalent in the calcite mudstones which are so 
abundant throughout C, and 8. Gurvanella tubules are seen 
forming the centre round which some of the oolitic grains in the 
lower part of D, have formed. Aphralysia was found in C, and 
S, (d). 
The algal material commonly tends to form nodules, but in 
K,, it also occurs as narrow layers interbedded with gritty bands, 
and in §, the Spongiostroma masses tend to form undulating sheets. 
In §,, especially in the lowest beds, the Seminula pisolite type 
prevails, characterized by the Spongiostroma and sometimes 
Mitcheldeania layers being arranged concentrically, often round 
Seminule. Lastly the Concretionary Beds of the top of S, form 
the most important of the algal developments, Mitcheldeamia being 
the prevalent form. 
(2) Foraminiferal Limestone——Foraminifera first begin to be 
fairly common in Z,. They are abundant in the Caninia oolite 
and are seen frequently in non-dolomitized bands (whether 
belonging to the calcite-mudstone series or to the oolites) in C, and 
the whole of S. They occur in great abundance in the white 
limestones of the upper part of 8,, and the lower part of D,. They 
abound in the pseudobreccias. Calcisphaera first becomes plentiful 
ama Zi. 
(3) Coral Limestone.—Zaphrentid corals play an appreciable 
part as limestone builders throughout. the Zaphrentis zone, and 
there is a well-marked Caninia band in §,. Bands full of Lztho- 
strotion martini are most characteristic of the S beds, and there 
is a well-known band of basaltiform Jxthostrotion in §,. The 
abundance of corals in the D beds is so familiaz that it need not 
be emphasized. 
(4) Crinoidal Limestone.—Crinoids occur in_ considerable 
abundance throughout practically the whole Lower Avonian, 
except in the Modiola shales and Caninia oolite, but are specially 
plentiful in (a) the Bryozoa Bed, (b) K, and K,, (c) the petit granite 
of the whole Zaphrentis zone. In the Upper Avonian crinoids are 
not specially characteristic, but occur in some abundance, and often 
reach a very large size in the white limestones of the D beds. 
Sections of echinid spines presumably to be attributed to Palechinus, 
