Retrospective Criticism. 463 
From many repeated observations, I am satisfied as to the correctness of 
the explanation I ventured to give of the cause of the splendid appearance 
of this minute vegetable. Indeed, a person acquainted with the laws of 
optics, as exhibited in lenses, would, on examining its structure of innu- 
merable perfect globules filled with a highly pellucid green fluid, have pro- 
nounced, @ priori, that they would condense the rays of light, and appear 
luminous to an eye placed in the angle of incidence, and the fact that it is 
always most brilliant, either in the cave or in a room with only a single 
window, when the face is turned from the light, ¢ustrates the theory in a 
singular manner. 
I have no hesitation in referring this beautiful moss to the order A’lgze, 
of which it will probably be found to belong to the tribe ConfervGidee ; but 
I must leave it to those who are better acquainted with this obscure family 
to decide whether it has yet obtained a name and a place in the system of 
modern cryptogamic botanists. —J. £, Bowman. The Court, near Wrea- 
ham, June 3. 1830. 
Geological Errors. — In p. 67. you give, in fig. 15., a sketch to show the 
relative position of the secondary rocks, which is taken from one of Dr. 
Buckland’s sections given in the fourth volume of the Transactions of the 
Geological Society, to illustrate his description of the groups of slate and 
greenstone rocks, which occur in Cumberland and Westmoreland, at the 
base of the great escarpment of Crossfell. The error has probably arisen 
from confounding the two colours used to show the “ whin sill”? in the 
midst of the mountain limestone beds, and the belt of greenstone rocks 
which accompany the slates and porphyries, through nearly their whole 
course ; perhaps, also, some confusion may have occurred from the term 
“ trap”? being used in the description on the plate; but, from whatever 
source it arises, an attention to the description in the text would clearly 
have explained Dr. Buckland’s meaning. In your Magazine, the green- 
stone is designated “ trap or whin sill;” from which it might naturally be 
inferred, that it was a portion of the whin sill which is found in the escarp- 
ment above, more especially as there are beds of mountain limestone, 
sandstone, and coal reposing upon it. This would be a great error, as it 
has no relation to that bed, but is merely, as Dr. Buckland describes it, a 
greenstone, whose varieties, from the different proportions of its ingre- 
dients, are almost endless. Having twice had an opportunity of examining 
this singular group of rocks in the course of my observations on the “ whin 
sill,” I cannot refrain from offering my humble tribute of praise to Dr. Buck- 
land, for the clear and accurate description he has given of them. I would, 
besides, take the present opportunity of saying a few words upon the old red 
sandstone, which occurs here, well defined, although of inconsiderable thick- 
ness.* The error into which Forster fell, in his section of the strata, by con- 
founding the old red conglomerate with the new red sandstone formation of 
* It isa singular thing, that Smith, in his geological maps of Cumberland 
-and Westmoreland, does not notice the old red sandstone of the foot of 
Crossfell, 
HH 4 
