AFrARENTLY CORRELATED TO THE CONDITION'S OF LIFE. 
307 
100 yards across, falling about 10 feet in level. On it also are many paired shells in 
situ. These shells differ considerably from those of the third terrace, being much 
thinner and more highly coloured {vide Table of Weights). The grooving on the 
inside of the shells is generally well marked in all behind the 7th rib. 
There are generally only about 17 to 19 well maiked ribs, the remainder being 
slightly indicated on the purple posterior surface of the shell. Most of the shell i.s 
purple behind about the llth rib, and the whole shell is suffused with pinkish-purple 
(see Plate 26, fig. 4). 
In 30 shells whose lengths vary between 26 mm. and 18 mm., the average ratio of 
length to breadth is 1 ; 0'730, and, taking 30 shells from 16 mm. to 21 mm. long, this 
average ratio is 1 ; 0'735 ; tliat is to say, that the average breadth of a shell 20 mm* 
long would be 14*7 mm. The beaks are reduced in size. 
The Fifth Terrace is a similar stretch of sand ; it is 200 yai’ds wide, falling nearly 
20 feet, and upon it are very many paired shells placed on their oral faces, like the 
others. These shells are much thinner than those of the fourth ,.errace. They have 
15 to 17 well marked ribs, and almost the whole shell is purple in colour in some 
specunens, but in others the first 3 ribs remain yellowish. The ribbing on the inside 
of the shell is generally apparent behind the 4th or 5th rib. The beaks are still 
further reduced in size. 
In 30 shells between 27‘5 mm. and 21 mm. in length the average ratio, of length to 
breadth is 1 : 0'731 ; and in 30 shells between 21 mm. and 16 mm. long this average 
ratio is 1 : 0’743 ; that is to say, that the average breadth of a shell 20 mm. long is 
14'8 mm., not materially differing from those of the last terrace. This terrace ends 
with the shelving sand. Below it are mud flats, the upper part of which is covered 
with heaps of muddy sand, cemented together with salt, forming the Sixth Terrace. 
The shells upon it, however, do not difter materially from those of the last, except, 
perhaps, in being rather thinner. 
Below it is the lowest level at which shells are found {Seventh Terrace). This level 
is 8 to 10 feet below that of the fifth terrace, and distant from it about 200 yards. 
Upon this lowest level-are several (five) concentric ridges, composed of shells washed 
up and partially cemented together with oxide of iron. The shells of which these 
ridges are made are like those of the fifth and sixth terraces. On the flat mud 
between these ridges, especially between the fourth and fifth, are great numbers of 
small paired shells placed on their oral faces. These shells are those of the last 
Cockles which lived, in the lake before it was dried up. At this time the water must 
have been very salt indeed, as the salt bed itself is about 5 to 6 feet lower and 300 
yards distarit. 
The shells are very small. The largest paired shell found in this place was 21 mm. 
long. They have 14 to 15 distinct ribs, are very thin, and of an almost uniform purple 
colour. The grooves between the ribs are all marked on the inside of the shell as 
2 R 2 
