148 F. Kingdom Ward — "Land of Deep Corrosions." 



base of a vertically placed wear facet on the inner side of the main 

 cusp. This tooth is obviously derived from a type similar to that 

 behind it by the increase in size of the eingulum. 



If we now turn to Biademodon entomopJiomis, Seeley, we find that 

 the hind upper molar agrees in its section with the penultimate molar 

 of. D. broiv?ii; the crown is most unfortunately destroyed. The 

 penultimate molar of D. entomophonus shows a further advance; 

 there is still the large main cusp with a smaller posterior cusp, and 

 the eingulum has grown considerably larger, but still supports the 

 original two cusps on its inner side. If we compare this tooth with 

 the corresponding tooth of D. mastacus we see a further change in the 

 same direction ; there is still the same main cusp with a smaller 

 posterior cusp, but the eingulum is still further exaggerated and now 

 has a small anterior in addition to the two original cusps. This tooth 

 is identical in structure with the much worn antepenultimate molar 

 of D. hrowni and is a typical Biademodon molar. 



It must be clearly understood that these three species, which occur 

 together, do not stand in any phylogenetic relation to one another, 

 but the series seems to give a clear idea of the origin of the upper 

 molars of Biademodon, the ' protocone ' being the antero-external 

 cusp and the whole of the inner part of the crown developed by the 

 hypertrophy of the eingulum. If this is the case for the upper 

 molars, it will also follow for the lower teeth, because the main cusp 

 of the upper molar always bites outside the whole lower tooth, and 

 if the lower molar had developed in the reverse way to the upper it 

 would bite into an exaggerated external eingulum. It is remarkable 

 that the view of the origin of the crown of the Biademodon molar put 

 forward above agrees exactly in its general lines with the theory 

 of mammalian molar development supported from embryological 

 evidence by M. F. Woodward and from the analogy of the premolar 

 development by many American palaeontologists. 



II. — Geological Notes on the "Land of Deep Corrosions". 



By F. KiNGDON Ward, B.A., F.R.G.S. 



(PLATES V AND VI.) 



A YEAR spent amongst the high mountain ranges of the Yunnan- 

 Tibet frontier, where the Sal ween, Mekong, and Yangtze Rivers 

 have been pinched together till they now flow parallel to one another 

 for 200 miles in a belt of mountainous country averaging about 

 75 miles in width, enabled me, while prosecuting my botanical 

 exploration, to ascertain a few facts of geological interest which 

 form the subject of the present paper (see Plates Y and YI and 

 Figs. 1-4). The Tibetans of Kham, with more eye for the 

 picturesque than one would have given them credit for, have, with 

 amazing intuition, appreciated the subtle distinction between a land 

 of high mountains and a land of deep valleys, and in their classical 

 writings refer to Tibet under the name of Nam-grog-chi, which, 

 according to Mr J. H. Edgar, may be translated "the land of deep 

 corrosions " ; and this it undoubtedly is. 



