Hetrospective Criticism, 4^63 



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, a 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 

 w^indow, when the face is turned fro7n the light, illustrates the theory in a 

 singular manner. 



I have no hesitation in referring this beautiful moss to the order A^lgse, 

 of which it will probably be found to belong to the tribe Confervoideae ,• 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. E. Bowman. The Courts near Wrex- 

 ham, June's. 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 aijove, 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 is a singular thing, that Smith, in his geological maps of Cumberland 

 and Westmoreland, does not notice the old red sandstone of the foot of 

 Crossfell. 



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