312 THE MICROSCOPE AND ITS REVELATIONS. 



number and course of the canaliculi ( 653), the nature of even a minute 

 fragment of Bone may often be determined with a considerable approach 

 to certainty; as in the following examples, among many which might be 

 cited: D r . Falconer, the distinguished investigator of the fossil remains 

 of the Himalayan region, and the discoverer of the gigantic fossil Tor- 

 toise of the Sivalik hills, having met with certain small bones about 

 which he was doubtful, placed them for minute examination in the hands 

 of Prof. Quekett, who informed him, on Microscopic evidence, that they 

 might certainly be pronounced Eeptilian, and probably belonged to an 

 animal of the Tortoise tribe : and this determination was fully borne-out 

 by other evidence, which led Dr. Falconer to conclude that they were 

 toe-bones of his great Tortoise. Some fragments of Bone were found, 

 many years since, in a Chalk-pit, which were considered by Prof. Owen 

 to have formed part of the wing-bones of a long- winged sea-bird allied to 

 the Albatross. This determination, founded solely on considerations 

 derived from the very imperfectly-preserved external forms of these frag- 

 ments, was called in question by some other Palaeontologists; who thought 

 it more probable that these bones belonged to a large species of the extinct 

 genus Pterodactylus, a flying lizard whose wing was extended upon a 

 single immensely-prolonged digit. No species of Pterodactyle, however, 

 at all comparable to this in dimensions, was at that time known; and the 

 characters furnished by the configuration of the bones not being in any 

 degree decisive, the question would have long remained unsettled, had 

 not an appeal been made to the Microscopic test. This appeal was so 

 decisive, by showing that the minute structure of the bone in question cor- 

 responded exactly with that of Pterodactyle bone, and differed essentially 

 from that of every known Bird, that no one who placed much reliance 

 upon that evidence could entertain the slightest doubt on the matter. 

 By Prof. Owen, however, the validity of that determination was ques- 

 tioned, and the bone was still maintained to be that of a Bird; until the 

 question was finally set at rest, and the value of the Microscopic test 

 triumphantly confirmed, by the discovery of undoubted Pterodactyle 

 bones of corresponding and even of greater dimensions, in the same and 

 other Chalk quarries. 



706. The application of the Microscope to Geology is not, however, 

 limited to the discovery or determination of Organic structure; for, as 

 has been now satisfactorily demonstrated, very important information 

 may be acquired by its means respecting the mineral composition of Rocks, 

 and the mode of their formation. The Microscopic examination of the 

 sediments now in course of deposition on various parts of the great 

 Oceanic area, and especially of the large number of samples brought up 

 in the ' Challenger ' soundings, has led to this very remarkable conclu- 

 sion, that the debris resulting from the degradation of Continental 

 land-masses are not carried far from their shores, being entirely absent 

 from the bottom of the deep Ocean-basins. The sediments there found, 

 where not of Organic origin, mainly consist of volcanic sands and ashes, 

 which are found in Volcanic areas, and of clay that seems to have been 

 produced by the disintegration of masses of pumice (vesicular lava), 

 which, after long floating, and dispersion by surface-drift or ocean cur- 

 rents, have become water-logged and have sunk to the bottom. As no 

 ordinary siliceous sand is found anywhere save in the neighborhood of 

 Continents and Continental islands, and as all Oceanic islands are the 

 products of local Volcanic outbursts, this absence of all trace of submerged 

 Continental land over the great Oceanic area, affords strong confirmation 



