140 Correspondence — Sir R. Owen — Mr. W. J. Black. 



usually ascribed — such as crystallization, pressure acting on con- 

 cretions in the process of formation, or chemical deposition of 

 sediment — will ever explain the points of structure and other 

 characters seen in the specimens that I have selected for description. 



Hunterian Museum, John Young. 



University, Glasgow, Jan. 5th, 1886. 



ON A NEW PERISSODACTYLE UNGULATE FEOM WYOMING. 



Sir, — In the Geological Magazine for February, 1886, it is 

 stated, p. 50, that no Perissodactyle mammal was known " to possess 

 tubercular teeth." Professor Cope does not supply the characters to 

 which his term ' tubercular ' is applicable. If he would kindly 

 refer to p. 362 of my "Palaeontology" (2nd ed. 1861), enlarged 

 views of the molars of both jaws of a genus of Perissodactyles 

 (Pliolophus), from Eocene, will be found. A still earlier example 

 of •'tubercular' molars, in the geuus Hyracotherium, is described and 

 figured in " British Fossil Mammals and Birds," 8vo., 1846, p. 422, 

 cut 166 : also from the 'London Clay.' 



Permit me to add that my estimate of the claims of Elephants and 

 Mastodonts to rank as an 'Order' rests upon the multilamellate 

 structure, size and succession of their ' grinders,' subordinate to 

 which dental character may be cited a vertebral one, necessitating 

 their special instrument the proboscis. The pentadactyle character 

 is common to Proboscidia with many Rodent genera, as well as with 

 the older Eocene members of the Coryphodont family, characterized 

 by Lophiodontoid modifications of the true molars. These teeth 

 afford the truest indications of affinity in the Ungulate series. The 

 diminutive Rhinocerontoid represented by the genus Hyrax as little 

 determines by molar characters an ordinal distinction form Acero- 

 therium as do the modifications of teeth and limbs in Bradypus 

 support an ordinal distinction in the Megatherioid family. 



Richard Owen. 



THE "ALASKA GLACIER." 



Sir, — In reference to the description of the Great Glacier in 

 Alaska, in "Nature" (Jan. 28th, 1886), I may draw attention to 

 the letter of Mr. J. Melvin in the same number, which would appear 

 to throw light on the subject of the progressive changes in it. The 

 ridges delineated in the diagram of the Glacier as lying between the 

 body of the Ice and the hill- side would seem to be analogous to the 

 Parallel Roads in Norway valle3'S, only they are formed on the flat 

 instead of the slope. 



The body of the Glacier seems evidently to have contracted itself 

 in consequence of loss of substance by melting underneath, and 

 withdrawn itself by these decided starts from the hill-side, and left 

 the ridges as relics of its foundations on the bottom of the valley. 



Probably the Glacier ages ago was quite flat on the top, and 

 reached across to the top of the morainic slope on the hill-side, and 

 it has since lost great bulk below by ground melting, which by 

 overstretching has caused the cracks or crevasses on the upper 



