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The observations, on which naturalists have founded that opinion of originality in some of the component parts of our earth, are these; first, They observe certain great masses of granite in which stratification is not to be perceived; this then they say is an original mass, and it is not to be derived from any natural operation of the globe; secondly, They observe considerable tracts of the earth composed of matter in the order of stratification as to its general composition, but not as to its particular position, the vertical position here prevailing, instead of the horizontal which is proper to strata formed in water; this, therefore, they also term primitive, and suppose it to be from another origin than that of the subsidence of materials moved in the waters of the globe; lastly, They observe both strata and masses of calcareous matter in which they cannot distinguish any marine body as is usual in other strata of the same substance; and these calcareous masses being generally connected with their primitive mountains, they have also included these collections of calcareous matter, in which marine bodies are not observed, among the primitive parts which they suppose to be the original construction of this globe.

For us, we could only give a hasty look at its southern volcanic cliffs; while we regretted that we could not inspect the marine strata of the eastern parts of the island, with their calcareous marls and limestones, hardened clays and cherts, and famous silicified trees, which offer important problems to the geologist, as yet not worked out.

The scoriaceous fragments and the calcareous matter are associated in the most irregular manner, sometimes in obscure beds, but more generally as a confused breccia, the lime in some parts and the scoriae in others being most abundant.

The calcareous strata of the Scotch coal-fields, those of Lanarkshire, the Lothians, and Fife, for example, are very insignificant in thickness when compared to those of England. They consist of a few beds intercalated between the sandstones and shales containing coal and ironstone, the combined thickness of all the limestones amounting to no more than 150 feet.

On the shores of Quail Island, I found fragments of brick, bolts of iron, pebbles, and large fragments of basalt, united by a scanty base of impure calcareous matter into a firm conglomerate.

The aspect of this part of the country during most of the year is of a light yellow color; for some months during the rainy season it is of a pleasant green mixed with yellow. Ranges of hills appear in the west, but east of them we find hundreds of miles of grass-covered plains. Large patches of these flats are covered with white calcareous tufa resting on perfectly horizontal strata of trap.

The skull on the board is of especial interest on account of the beautiful crystals of calcareous spar, which are from 1/10 to 1/4 of an inch long, and are formed on the inner sides of the skull. The skull is 5-1/2 in. wide between the fangs and 6-3/5 in. wide at the forehead, whereas the skull of the skeleton is only 3-9/10 in. wide at the fangs and 5-1/10 in. wide at the forehead.

The last two hours were notable for a heavy fall of rain, and, about half past five, we reached a solitary house occupied by friendly people, where we took up our quarters for the night. Within ten minutes we glided past the last waterfall, between white calcareous rocks of a kind of marble, covered with magnificent vegetation. The latter give their names to the lower portion of the stream.

Between these points and Mercedes on the Rio Negro, there are scarcely any good sections, the road passing over limestone, tosca-rock, calcareous and bright red sandstones, and near the source of the San Salvador over a wide extent of jaspery rocks, with much milky agate, like that in the limestone near San Juan.

In the former large spaces consist of sand and SOFT CLAY; and Kotzebue speaks of clay having been found within one of the Marshall atolls. No doubt this clay is calcareous mud, similar to that at Keeling Island, and to that at Bermuda already referred to, as undistinguishable from disintegrated chalk, and which Lieutenant Nelson says is called there pipe-clay.