226 
The contemporaneity of man, and the extinct mammalia as 
an argument for man’s antiquity is virtually given up, if it is 
admitted that these mammals were not extinct 9,750 years 
ago, and yet I can reach no other conclusion from Mr. Pengelly’s 
own estimate of stalagmitic rate of accretion applied to Mr. 
Pengelly’s own statement of facts. 
We must now ask a question about the uniformity of stalag- 
mitic accretion,* and we shall be helped in that inquiry by Mr. 
Pengelly’s own description. It is as follows : — “ The roof of the 
cavern is of limestone, and through it in rainy weather the water 
percolates slowly in most cases, but sometimes more rapidly. 
That water contains carbonic acid. It is by that carbonic acid 
that the water dissolves the limestone which constitutes the 
roof. It reaches the inner surface of the roof, and hangs there 
as a drop. You come into the cavern and hear a drop here and 
a drop there, and you know what process is going on. The lime- 
stone has been dissolved overhead, and as the water falls it brings 
a particle of the limestone to the floor, where it is precipitated. 
It sooner or later forms a little boss, more or less conical ; thence 
it flows away, and meeting that flowing from other such bosses, 
a sheet is ultimately formed, which covers the entire floor. 
This is stalagmite. The stalagmitic sheet cannot be formed 
more rapidly than the limestone is dissolved, which again is the 
function of the amount of carbonic acid in the water.”! Could 
any description be better ; at the same time it points to a probable 
cause of non-uniformity ; for anything which could cause an 
increase or decrease in the amount of carbonic acid in the water 
woidd hasten or retard the accretion of the stalagmite. I 
suggested in Nature , January 1st, 1874, “ that when the thick 
forest (the habitat of the animals whose hones were found in the 
cave) left an accumulation of decayed vegetation on the soil, 
we had the natural laboratory where the rain would find the 
carbonic acid to act as a solvent upon the calcareous earth ; but 
as by the axe of man the forest decreased, in that proportion 
the chemicals lessened, and, as a consequence, the deposit 
diminished.” 
Mr. Pengelly in an address at Teignmouth, July, 1874, 
replied to the above by producing Liebig’s chemical analysis of 
various kinds of vegetation, showing that equal surfaces of cul- 
tivated land of an average fertility are capable of producing 
equal quantities of carbon, whether it consists of trees, corn, 
* Mr. Howard has some valuable remarks upon this subject in his paper 
read before this Institute on the Torquay caverns. 
f Kent Cavern , its Testimony to the Antiquity of Man, December, 1875, 
pp. 8, 9. 
