Lacustrine Formation of Tomyburn V alley. 9 
pouring into the lake ; but as soon as this ceased, these plants 
immediately took full possession of the lake in advance of the 
arrival of the molluscan fauna, and even after this addition to the 
living forms which peopled the lake, the lacustrine vegetation 
formed a predominating element in the deposit made at its bottom. 
After the arrival of the mollusca, however, the species of plants 
were not all the same as those which lived in the lake before that 
time, but included forms better suited to the clear, calcareous waters 
in which the water-snails delighted. Such plants, too, as were now 
in the lake had a better hold of their habitat, flourished in great 
numbers, and the species were not replaced with the same rapidity as 
their predecessors had been. 
OBSERVATIONS ON THE CHARACE^. 
The Charm participated in the conditions eftecting other portions of 
the lacustrine vegetation, and their appearance in the lake at a 
very early period is noticable and somewhat remarkable. These 
plants are of a comparatively low order, and entirely aquatic in habit. 
They live submerged in the water, their seeds are not adapted for being 
wafted by the wind, and the disagreeable odour, which characterizes 
the living plant, would repel many animals, which are active in pro- 
pagating other plants, by transporting their seeds from place to place ; 
yet a species of this genus was one of the earliest migrants into the 
lake. 
The permanency of Chara when it has once taken possession of a 
sheet of water may be inferred from the fact that difierent species 
flourish in lakes in the same neighborhood without intermixture for 
(historically) long periods of time — a lake having one or more species 
or varieties peculiar to itself. The early advent of Chara at Lawlor’s 
Lake is therefore somewhat remarkable. It is true that some species 
of this genus inhabit brackish water ; but the relations of Lawlor’s 
Lake to the surrounding land show that at its emergence from the 
sea, the transition from salt to fresh water conditions must have 
been rapid, if not instantaneous. 
Though the stems and leaves of Chara are perishable, the small 
nucleus or spores, which are about the size of a minute pin-head, are 
hard and durable ; and owing to the spiral strim or keels (due to the 
impression of the spiral tubes of the sporangia or seed vessel) with 
