40 
Correspondence — Prof. A. H. Green. 
of these objects radiating tbeir heat more rapidly tlian the sur- 
rounding air, and because they are solid forms presented to a liquid 
at the moment of crystallization, tbe feathers of the hoar frost ex- 
tending to windward as each particle of wateris driven by tbe breeze 
and frozen upon it. 
So in a stream of water at the freezing-point, the stones at the 
bottom no doubt radiate tbeir heat more rapidly tlian the surround- 
ing medium, and particle after particle of water assumes its crystalline 
form on coming in contact with the solid, thus forming tubulär 
masses in the direction of the stream. 
124, 'Wincheaf, Canterbury. S. Gordon McDakin. 
PEOF. NORDENSKIÖLD ON RECURRENT GLACIAL PERIODS. 
Sir, — Prof. Judd lias told us repeatedly of late, not without some 
flourish of trumpets, how completely Prof. Nordenskiöld lias de- 
molished Mr. Croll and bis theory of the causes of glacial epochs. 
Now from my youth up 1 liave been backwai-d in my reading, and 
have had an unconquerable aversion to books, and never read any- 
thing myself, if I can get a kind friend to read it for me, and teil 
me what it is about. So I have not yet read Prof Nordenskiöld ; 1 
Prof. Judd is evidently thoroughly well up in him, and he would be 
doing a great kindness to myself, and perhaps otliers who are equally 
ignorant and lazy, if he would send you a short article giving Prof. 
Nordenskiöld’s facts and arguments. Prof. Judd says tbese do not 
support Mr. Croll’s theories ; but what I especially want to know is, 
whether there is anything in them that teils against the generally 
received views on the subject. 
Yorkshire College of Science, Leeds. A. H. Green. 
Dec. 9th, 1876. 
GLACIAL ORIGIN OF LAKES. 
Sir, — I have to aslc for space for a reply to the courteous letters of 
Mr. Bonney and of my friend Mr. Judd. 
Mr. Bonney’s letter is mainly explauatory of his position, whicli 
several circumstances — unnecessary to detail — combined to render 
somewhat ambiguous. I think comparison would tend to show that 
1 The paper by Prof. Nordenskiöld especially referred to by Prof. Judd, is “ On 
tbe Former Climate of tbe Polar Regions,” being an address by Prof. Nordenskiöld 
delivered at the Anniversar)' Meeting of tbe Royal Swedish Academy of Sciences, 
March 31, 1875, and translated and printed in full in tbe Geological Magazine, 
1875, Dec. It. Vol. II. p. 525. Tbe passagc quoted by Prof. Judd nppearsatp. 531, 
but tbe whole paper is well worthy of perusal; as is also his paper “ On the Geology 
of Icefiord and Bell Sound, Spitzbergen,” Geological Magazine for 1876, pp. 16, 
63, 118, 255. Perhaps Prof. Green will “get a kind friend to read them for bim.” 
Nordenskiöld’s “ Expedition to Greenland ” also appeared in the Geol. Mag., 1872, 
Vol. IX. pp. 289, 355, 409, 449, 516, and has some good materials in it bearing on 
the former climate and the extinct floras. Many of our readers, when oppressed with 
tbe wearisome effort to master the contents of our montbly issue, wül cordially sympa- 
tbize with Prof. Green, and wisli for a mental digester and Assimilator like the 
Artificial Stomach in the Loan Collection) into which, as into a “ Papin’s Digester,” 
they migbt put their heavy reading, and so get therefrom the extractum xenxorum in 
a concentrated form. Till tbis invention is patented, Prof. Green has hit upon a 
happy expedient: “ Get a kind friend to teil you what it is about” ! — Edit. Geol. Mag. 
