ICE 



[226 ] 



I C H 



t)f 300 feet, and as it has been as- 

 certained that for every foot above 

 the surface of the sea- water there 

 are eight feet below, the whole 

 thickness must be immense. In a 

 geological point of view, icebergs 

 are to be viewed as very important 

 and powerful agents, inasmuch as 

 they are the means of transporting 

 to great distances, animals, plants, 

 and rocks. 



ICE- SPAR. So named from its resem- 

 blance to ice. A mineral occurring 

 both massive and in flat crystals. 

 It is found at Mount Somma, near 

 Naples. 



ICHTHY'ODON. The name used by some 

 authors to designate a tooth of any 

 fossil fish. 



ICHTHYODO'EULITE. The fossil dorsal 

 spine of certain fishes, armed with 

 tooth-like hooks, or prickles. These 

 were long supposed, says Professor 

 Buckland, to be jaws, and true 

 teeth; more recently they have 

 been ascertained to be dorsal spines 

 of fishes, and, from their supposed 

 defensive office, have been named 

 ichthyodorulites , from the Greek 

 words txOvs, a fish, Sdpv, a spear, 

 and X/0os, a stone. The icthyodo- 

 rulites of the old red sandstone, 

 observes M. Agassiz, belong to 

 distinct species of the genera oncTius 

 and ctenacanthus. These bony 

 spines are more or less arched, and 

 grooved by longitudinal furrows, 

 separated by round ridges forming 

 ribs. The great distinction between 

 this genus of Ichthyodorulites, and 

 the large species of Hybodus of the 

 lias and new sandstone, to which 

 they have some resemblance in the 

 arrangement of their longitudinal 

 furrows, is, that their posterior 

 edge has no sharp points or teeth, 

 while in the genus hylodus there 

 are on that side strong points which 

 are arched downwards. Murchison. 

 That highly talented, and much 

 to be lamented author, the late 

 Hugh Miller, says, " there occa- 



sionally turn up, in the sandstones 

 of Perthshire, ichthyodorulites that 

 in bulk and appearance resemble 

 the teeth of a harrow, rounded at 

 the edges by a few months wear." 



I'CHTHYOLITE. (from ixOvs, and \iOos, 

 Gr. ichtyolite, Fr.) The name given 

 to any fossil fish ; a petrified fish. 

 Fossil fishes occur in all the Eng- 

 lish formations, from the old red 

 sandstone to the tertiary deposits 

 inclusive. 



ICHTHYOLI'TIC. Pertaining to fossil 

 fishes, as the ichthyolitic formation. 

 " In the ichthyolitic formation, im- 

 mediately over the Silurian, that 

 of the old red sandstone, the ganoids 

 first appear." Hugh Miller. 



ICHTHYO'LOGY. (from IxQvs, a ^ sn * 

 and Xo<yo?, Gr. discourse; ichtyo- 

 logie, Fr. ictologia, It.) That 

 branch of zoology which treats of 

 the structure, classification, habits, 

 and history of fishes. The study 

 of fossil ichthyology, says Prof. 

 Buckland, is of peculiar importance 

 to the geologist, as it enables him 

 to follow an entire class of animals, 

 of so high a division as the verte- 

 brate, through the whole series of 

 geological formations; and to in- 

 stitute comparisons between their 

 various conditions during successive 

 periods of the earth's formation. 

 Professor Agassiz has already ex- 

 tended the number of fossil fishes 

 to two hundred genera, and eight 

 hundred and fifty species. No ex- 

 isting genus is found among the 

 fossil fishes of any stratum older 

 than the chalk formation. 



ICHTHYO'PHAGOUS. (from /X^S, & fish, 



and 0afyo>, Gr. to eat ; ichthyophage, 

 Fr. colui che non si ciba d'altro 

 fuorchb di pesci, It.) Feeding on 

 fish. 



ICHTHYOSATJR. ] (fl'Om X^ S a ^ 8D > 

 ICHTHYOSAURUS. ) and ffavpos, Gr. 



a lizard.) A fish-like lizard; an 

 immense fossil marine- saurian or 

 reptile, having an intermediate 

 organization between that of a 



