2 R. M. Deeley—Trail and Underplight. 
more tolerant of cold, were alone able to pass into North-Eastern 
Asia, while the llamas of the time were better fitted to pass through 
the 'ropics to South America, where fossil forms have been found in 
Ecuador and Brazil. In the later Pleistocene the group became 
totally extinct in North America, hence its peculiar discontinuous 
distribution at the present day. 
The earliest genus that can with certainty be referred to the 
Tylopoda is Protylopus from the Upper Eocene (Uinta). This genus 
includes animals about the size of a hare, in which the full dentition 
of 44 teeth was present, the bones of the fore-arm were separate, 
the fibula was complete, and there were four functional digits 
in each foot. In the White River Beds (Lower Oligocene) the 
genus Poébrotherium is represented by several species, some of which 
attained the size of a sheep. In this genus also the full dentition was 
present, but the selenodont molars were becoming high-crowned, the 
fibula was incomplete, and there were only two functional digits in 
each foot, although remnants of the others persisted. Up to this stage, 
according to Professor W. B. Scott, only one phylum is traceable, but 
in the Lower Miocene the group gives rise to two side branches, one, 
the gazelle-camels, of which Stenomylus is a representative, and the 
other, the curious giraffe-camels, which, as their name implies, 
possessed very long neck and limbs and probably browsed on trees 
like giraffes. The earlier (Lower Miocene) form Oxydactylus was much 
smaller than the later Alticamelus, and its neck and limbs were less 
elongated. The grazing camels, which may be regarded as the main 
stock of the group, possessed selenodont molars with increasingly high 
crowns, and in the later forms both in this group and in the giraffe- 
camels the metapodials fuse to form cannon-bones, the bones of the 
fore-arm unite, and the fibula is greatly reduced. Procamedus of the 
Upper Miocene of North America seems to represent approximately 
the common ancestor of camels and llamas. The earliest members of 
the sub-order yet found in the Old World are from the Lower Pliocene 
of the Siwalik Hills; other forms existed in the late Pleistocene and 
perhaps in Neolithic times in Northern Africa. In Europe remains 
of Pleistocene camels have been found in Southern Russia and 
Rumania. 
IJ.—Trait anp UNDERPLIGHT. 
By R. M. DEELEY, M. Inst.C.E., F.G.8. 
{J\HE peculiar features presented by the upper or land-surface 
I portions of some deposits, or rather those portions of certain 
deposits which are now, or have been in times past, land-surfaces, 
have engaged the attention of many geologists. Most of those who 
have studied them are satisfied that some features which they often 
show are not now being produced in this country, and they are 
attributed by many observers to the action of different climatic 
conditions to those which at present exist. 
The form of disturbed surface deposit to which I particularly refer 
