528 Correspondence — Messrs. Dakpns, Sicks, McGee. 



pterygoid shows two kinds of dentition ; on its outer edge is a 

 single row of twenty-six large teeth of equal size, which, are some- 

 what smaller than those of the maxillary bone. Internal to these 

 on the anterior part of the pterygoid are from three to six irregular 

 rows of short pointed teeth similar to those on the parasphenoid. 

 In the under-jaw there are thirty teeth. 



This instalment of Dr. Fritsch's work leads us to look forward to 

 its subsequent progress with great interest. It is a monument 

 of conscientious labour and admirable skill in deciphering remains 

 in which the characters presented more than ordinary difficulty. 



H. G. Seeley. 



C O IRIRIE S IF O IITIDIE ZEsTC IE . 



THE PUEPLE BOULDEK-CLAY AT HOLDEENESS. 

 Sir, — In the excellent account of English glacial deposits, given 

 in the second edition of " The Great Ice Age," it is stated that " in 

 Holderness the purple clay is quite unstratified." It is true, that in 

 many places the "Purple Boulder-clay" is unstratified; but in many 

 others it is distinctly stratified. The stratified and unstratified por- 

 tions are, however, so mixed up together, and run so into one another, 

 as to be quite inseparable. The deposit has also been much shoved 

 about, the thrust having in some well-marked cases come from 

 the N.N.E. J. E. Dakvns. 



Driffield, Oct. 9th, 1879. 



ON THE CLASSIFICATION OF THE BEITISH PEE-CAMBEIAN EOCKS. 



Sir, — Will you kindly call attention to the fact that by some 

 mistake the word not has been left out after the word did in my 

 paper, p. 434, line 19 from bottom of page. The sentence should 

 read, " If these movements also did not take place, etc." As the 

 absence of this one little word does away with the proper meaning, 

 I shall feel obliged if you will kindly notice it in the next Number 

 of the Geol. Mag. Hv. Hicks. 



Hendon, N.W., Oct. 3, 1879. 



SUEFACE GEOLOGY OF THE MISSISSIPPI VALLEY. 

 Mr. "W. J. Mc Gee writes from Farley, Iowa, September 18, 1879, 

 in reference to his communication, which appeared in the Geol. 

 Magazine for August, pp. 353-362, and September, pp. 412-421 : — 

 " Thanks for your care in revising proofs of my paper in the Geol. 

 Mag. A very few errors have crept in, however, which I will note. 



W. J. Mo Gee." 

 Page 358 (August No.), line 30, for " mentioned " read " weathered." 

 ,, 359 „ „ v6, „ "mass" ,, "moss." 



„ 361 „ „ 33, „ "Level" „ "Lead." 



„ 414 (Sept. No.), „ 11, ,, "basalt" „ "basal." 



,, 418 „ in footnote, ,, "p. 168" ,, "p. 105." 



COLUMNAE SANDSTONE IN SAXON SWITZEELAND. 



We are requested by Mr. Walter Keeping to make the following corrections in his 

 article wbich escaped notice— namely, at p. 438, line 2 from foot, for ' binding' read 

 ' bending,' and on p. 441, line 8 from top, for ' Yorkshire,' read ' Derbyshire.' — 

 Edit. Geol. Mag. 



