And although, perhaps, a poet's authority to not the very best for a geological fact, I have the less hesitation in quoting his couplet, as it is, to a certain extent, corroborated by the circumstance that, amongst all the dangers and disasters recorded with so much minuteness by the historians of the first discoveries of those parts, there is no instance, that I am aware of, mentioned by them of a shipwreck in the river below San Gabriel, the port to which all vessels at that time directed their course after entering it:--from this I think any one who knows the dangers of the navigation of that part of the river now, will be disposed to infer that it really must have been in former times as Centenera describes it, much more free and safe than it is at the present day:--it is probable that the Ortiz bank especially has very much increased. [47] In the proportion of an ounce of litharge to a quart of oil. [48] The following comparative measurements of the bones of the megatherium and of an elephant eleven feet high, are furnished by Mr. Clift:-- ELEPHANT. MEGATHERIUM. Ft. In. Ft. In. The expansion of the ossa ilia 3 8 5 1 Breadth of the largest caudal vertebra 0 7 1 9 Circumference of middle of femur 1 0 2 2 Length of the os calcis 0 7-1/2 1 5 [49] Mr. Clift quotes a MS. memorandum in his possession, stating the measurement of the skeleton at Madrid to be, from the front of the nasal bones to the setting on of the tail, thirteen feet seven inches, and he is of opinion that, of the two, the specimen I brought home was the older and somewhat larger individual. CHAPTER XI. OF THE RIVERS PARAGUAY, PARANA, AND URUGUAY. Importance of the rivers of the United Provinces. The Paraguay and its tributaries. The Pilcomayo. The Vermejo. Soria's expedition down it from Oran, proving it navigable thence to Assumption. Periodical inundations of the Paranã, similar to those of the Nile. The Uruguay and its affluents. Surveys by the Commissioners appointed to determine the Boundaries laid down by the Treaty between Spain and Portugal of 1777. Original Maps obtained. Before proceeding to give any account of the Upper Provinces, a brief description will perhaps here not be out of place of the great rivers which form so remarkable a feature in the physical geography of this part of the South American continent, and from the navigation of which by steam-vessels hereafter such important political consequences may be anticipated.