EVIDENCES OF CHANGE OF LEVEL. 535 
level at C, which is the summit of the low ridge referred to. It is 
about ten feet higher than the first. From C there is a rapid slope to 
a lower level, which is occupied mostly by forests; and three to six 
miles back the land gradually rises into the Illawarra range. The 
shells of this beach-ridge are much broken, like seashore specimens ; 
but many are nearly entire, and generally the nacre is little injured. 
The form of these shores leaves little occasion for doubting that the 
upper ridge is actually the summit of an ancient beach, formed like 
the lower one (B). 
A large portion of Illawarra has been but lately reclaimed from the 
sea. ‘The former condition of the district, especially of the part north 
of Wollongong, appears to be well illustrated in the existing “ Illawarra 
Lake” and “Tom Thumb Lagoon.” Both of these lakes were once 
connected with the ocean by wide mouths; but for the four years 
past, the former, which is about six miles long by three broad, has 
been closed by sands thrown up by the sea, and now a sand-beach one 
hundred yards wide separates it from the ocean. ‘The water is gra- 
dually becoming fresh, and has already so far lost in saltness that the 
oysters, cockles, &c., formerly living there, are all destroyed. ‘The 
fresh-water streams running into it may again break down the bar- 
rier, as they have already raised the water two or three feet, and this 
has often taken place in former periods previous to its last closing. 
Thus salt-water and fresh-water formations might go on in many 
alternations without any change whatever in the level of the land. 
Tom Thumb is about one-third of the lineal dimensions of the Illawarra 
Lake. It has been closed, but is now open, though by so shallow achan- 
nel that we may pass along the beach by its mouth on horseback at low 
water during calm weather. Several of the existing marshes in Illa- 
warra are known to have been lakes. ‘The change to their present 
condition may have been hastened by a small elevation of the land. 
The Illawarra mountain range was probably once the line of coast. 
The advance of the shores by the gradual accumulation of sand from 
the sea is seen at Shoalhaven, where, for three-fourths of a mile back, 
the land is a low seashore accumulation of loose sand, in which shells 
are scattered. ‘The water for a long distance off the beach between 
Black Head and Shoalhaven is very shallow. A deposit of shells 
occurs half a mile from the Illawarra Mountain, west of Tom Thumb 
Lagoon; but we cannot confidently say that they were not carried 
there by the natives. 
On the borders of the Hunter and on its islands there are large 
