These three instances, in each of which there is a distinct reference to a gigantic form of tortoise, comparable in size with the elephant, suggest the question whether we are to regard the idea as a mere fiction of the imagination, like the Minotaur or the Chimæra, or as founded on a living tortoise. Dr. Falconer points out that it seems unlikely that such fables could have been suggested by any of the small species of tortoises now living in India, and consequently is inclined to think that the monster was seen by man many centuries ago, long before he began to write history. We have already alluded to the large number of mammalian forms of life that were contemporary with the Sivatherium and Colossochelys, but if we examine this old Sivalik fauna we find it presents several very interesting features. In the first place, it exhibits a wonderful richness and variety of forms, compared to the living fauna of India. Take the pachydermata, for instance--an old order established by Cuvier to include the rhinoceros, hippopotamus, elephant, etc.--and we find there were, in the period under consideration, about five times the number of species now known in India. Elephants and mastodons, too, of various species abounded. So it is with the ruminants; besides a large number of species allied to those now living, such as the ox, buffalo, bison, deer, antelope, musk-deer, and others, there were giraffes and camels, as well as the strange Sivatherium. And so it is with the other orders, such as carnivora, rodents, insectivora, etc. Secondly, this great and varied fauna of the past shows a striking resemblance to that of India at the present day. Darwin found the same resemblance in South America; and now it is accepted as a general law, that the living fauna of a country resembles its extinct fauna, especially that of the latest geological period. Dr. Falconer found that India's living fauna is but, as it were, a remnant of that which it once possessed. Thirdly, this extinct Sivalik fauna presents a singular mixture of old and new forms. And lastly, it points to a very different geographical distribution of animals. Thus the giraffe, the hippopotamus, and the ostrich are _now_ confined to Africa. Facts such as these serve to throw light on the geography of the past; but we cannot stay to enlarge on that subject here. Much might be said about the fossil elephants and mastodons from the Sivalik Hills, so fully described by Dr. Falconer, but since chapters xiii. and xiv. deal with elephants, we must reserve our remarks till then, only alluding here to one striking form from the Sivalik Hills, namely, the Elephas ganesa, the tusks of which were more than ten feet in length, and much less curved than those of the mammoth. A very fine specimen of the head and tusks may be seen in the gallery of fossil mammals in the Natural History Museum (Gallery I, Stand D).