Correspondence — Mr. W. J. Harrison — Jfr. B. M. Deeley. 567 



NEW LOCALITIES FOR THE MINERALS BROOKITE, NATEOLITE, 

 AND BARYTES. 



SiK, — I have recently discovered a new locality for Broolcite 

 and Natrolite in Caernarvonshire (the old locality is near Tremadoo). 

 The Gimblet rock, Pvsrllheli, consists of a compact ophitic dolerite 

 containing labradorite, large brilliant crystals of augite, and magnetite. 

 Fissures traverse the rock in all directions, and are filled with 

 quartz and calcite. Small bright crystals of Broolcite are imbedded 

 in the dolerite and project into the fissures ; they are in many 

 cases surrounded and covered by calcite, but are revealed on removal 

 of the latter by hydrochloric acid. The largest crystals have a 

 diameter of one quarter of an inch, and are tabular in habit : 

 the large faces are striated in the direction of the vertical axis. 



The mineral Natrolite occurs in geode-like cavities in the dolerite, 

 and is intimately associated with calcite and quartz. The radiating 

 spherical groups of Natrolite are white in colour, and from one 

 quarter to half an inch in diameter. 



Last August I had occasion to visit Dosthill, near Tamworth, and 

 am able to add a new mineral to the list of those hitherto known 

 as occurring in Warwickshire. The mineral is Barytes, and occurs 

 in veins an inch in diameter in the Cambrian shales. The crystals 

 have a beautiful reddish colour due to enclosed ferric oxide. 



122, LiNwooD Road, Handsworth, Birmingham. ^tt t tt.„„,„^„ t„., 

 Mv. Srd, 1894. W- J' HARRISON, J UN. 



GLACIAL GEOLOGY. 



Sir, — Although I scarcely think that Sir H. H. Howorth's letter, 

 published in your November Number, calls for any remark from me, 

 I cannot refrain from noticing a few of his arguments, as they 

 reflect strongly upon his controversial methods. 



It is an impertinence, it would seem, for me to say anything about 

 Switzerland and its glaciers, or to look at them, seeing that others 

 have already been there, and that a whole library was written upon 

 the subject before I was born! Indeed, it was an unjustifiable 

 public advertisement to say that I had ever been there or had even 

 seen a glacier ! At the same time he regards it as preposterous that 

 '• those who have never studied the mechanics of ice in a laboratory, 

 and, what is more strange, have never seen a glacier at all," should 

 write upon the subject. There is clearly no way out of the diffi- 

 culty ; I must do something preposterous or be impertinent, if I 

 am legitimately to interest myself in glacial matters ! 



His answer to the demand I made for a statement of the angle of 

 elope at which a glacier ceases to flow is equally characteristic. We 

 learn that Forbes " collected considerable evidence to show what 

 the least angle is upon which ice will begin to move. This is the 

 slope, the least slope, available." In other words it is "as much 

 again as half." 



We also learn that although the Antarctic continental ice may 

 move into deep water, and present a vertical wall of ice to the ocean 

 450 miles long and more than 150 feet high, to imagine that con- 



