256 EEPOET— 1880. 



Artesian "wells •svLicli are frequently bored never reach the bottom — with 

 a series of lacustrine deposits, earthy, clayey, and sandy. Most frequently 

 the alluvium contaius a great quantity of pumice and volcanic ash, and 

 then acquires so much consistence as to be used in the cheaper and less 

 durable kinds of building. A con^siderable area is covered by lakes, 

 Chalco. Xochimilco, Tezcocn, &c., and these, particularly the latter, have 

 diminished greatly since the Spanish Conquest. The principal lake, into 

 which all the others drain, Tezcoco, is very shallow, nowhere more than 

 fonr or five feet deep, and has no definite limits, but alters its area by 

 many square miles in the course of every season. It is easy to see that the 

 various lakes now scattered over the Plateau are merely the remnants of 

 one vast lake, whose shallow watei's extended over the vast plain around 

 the site of the City of Mexico, and which received the torrents which 

 come down from the surrounding mountains every rainy season laden 

 with detritus. Meanwhile the volcanoes, which are scattered over and 

 around the Plateau, were in great activity, and the surface of the lake 

 seems to have been generally either wholly or partly covered with pumice 

 and ashes, which as the waters receded during di'ougbt wonld be deposited 

 along with the mud at the bottom. 



It is interesting to compare the lava-flows Avhich have been emitted 

 on what was at the time dry land with those which were formed in the 

 lake itself. The former, such as the Pedregal de Thalpan, are dense, 

 hard, and black, like the lava of Vesuvius ; the latter, e.g. the two little 

 hills near ]\Iesico, known respectively as the Great and Little Peiion, are 

 gigantic cinders, red, cracked and porous, and here and there containing 

 large irregular caves, formed simply by the expansion of the included 

 water into steam. 



All over the Plateau, imbedded in the soft alluvium or in the denser 

 ' tipitate ' as the rock containing j^imice is called, and frequently laid 

 bare by the streams, are to be fonnd considerable numbers of mammalian 

 skeletons. To examine and collect these I made a good many expeditions, 

 generally accompanied by one or two Indians, who served as guides and 

 excavators. I obtained many sjjecimens, nearly all, however, in very 

 imperfect preservation, and many so friable as scarcely to bear removal. 

 The most abundant I'emains are those of Elephas. Mastodon, however, 

 occasionally occurs, and skeletons of horses, buffaloes, and wolves are 

 tolerably common. I was much interested by the fact that some time 

 before and again during my visit a specimen of Glyptodon, apparently 

 clavipes, had "been found in the course of some engineering work, and 

 had come into the possession of the museum there, thus establishing the 

 rano-e of this genus of Edentates into the northern part of the Neotropical 

 reo-ion. I was fortunate in discovering a magnificent Edentate skeleton, 

 closely resembling Myhdon ; but, on returning with my workmen early 

 next morning to continue the excavation, we found our specimen shattered 

 into fragments. Some of the country people, who always watched one's 

 movements with intense suspicion, and who alternately regarded us as 

 treasure-seekers and as magicians, so adding considerably to the danger 

 and discomfort of the undertaking, had done this, and we were able only 

 to rescue a single broken tooth, now in the British Museum. 



On my way home I examined, along with Mr. Halliday, C.B., of Vera 

 Cruz, an artesian well which he was boring in hopes of obtaining a supply 

 of water for that city. He had passed through 1260 feet of sands and 



