OLD 



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L I 



micaceous sandstone slate. In 

 some situations the old red sand- 

 stone attains a thickness of 2000 

 feet and upwards. 



" It was a prevalent belief among 

 geologists," says Sir E,. Murchison, 

 "that few or no animal remains 

 existed in the old red sandstone of 

 England. I first undeceived myself 

 on this point by observing shells in 

 the lower group, or tilestones, in 

 Caermarthenshire. I afterwards 

 discovered similar fossils in the 

 great outlier of Clun forest. The 

 old red system may now fairly be 

 said to be characterized throughout 

 by ichthyolites peculiar to it. The 

 rocks known to English geologists 

 under the name of the old red 

 sandstone, consist of various strata 

 of conglomerate, sandstone, marl, 

 limestone, and tilestone, the young- 

 est beds of which dip conformably 

 beneath the carboniferous deposits, 

 whilst the oldest repose upon and 

 pass into certain grey-coloured rocks. 

 These last form the upper part of 

 the Silurian system." 

 OLD EED SYSTEM. Sir R. Murchison 

 has applied this term to what has 

 heretofore been known as the old 

 red sandstone. ' ' Being convinced, ' ' 

 he says, "that the old red sandstone 

 is of greater magnitude than any of 

 the overlying groups, I venture for 

 the first time, in the annals of 

 British geology, to apply to it the 

 term system, in order to convey a 

 just conception of its importance in 

 the natural succession of rocks, and 

 also to show, that as the carboni- 

 ferous system, in which previous 

 writers have merged it (but from 

 which it is completely distinguish- 

 able, both by lithological characters 

 and zoological contents,) is sur- 

 mounted by one red group ; so it is 

 underlaid by another, this lower 

 group being infinitely thicker than 

 the upper." Sir R. Murchison 

 proposes to divide the old red system 

 into 1, Quartzose conglomerate 



and sandstone. 2. Cornstone and 

 marl. 3. Tilestone. He considers 

 the united thickness of the old red 

 system, at a moderate calculation, 

 to amount to nine or ten thousand 

 feet. 



" It will be found," says Hugh 

 Miller, "that this hitherto neg- 

 lected system yields in import- 

 ance to none of the others, whether 

 we take into account its amazing 

 depth, the great extent to which it 

 is developed both at home and 

 abroad, the interesting links which 

 it furnishes in the zoological scale, 

 or the vast period of time which it 

 represents. There are localities in 

 which the depth of the old red 

 sandstone fully equals the elevation 

 of Mount Etna over the level of the 

 sea, and in which it contains three 

 distinct groups of organic remains, 

 the one rising in beautiful progres- 

 sion over the other." See Tilestone. 



OLDEE PLIOCENE. Sir C. Lyell has 

 sub- divided the tertiary epoch into 

 four periods; namely, the newer 

 pliocene or pleistocene, the older 

 pliocene, the miocene, and the 

 eocene. The term pliocene he 

 derived from the two Greek words 

 ir\eiicv, more, and, KCUVO?, recent. 

 The older pliocene formations lie 

 between the miocene and the newer 

 pliocene or pleistocene. Of fossil 

 shells examined by M. Deshayes, 

 the older pliocene contained from 

 thirty- five to fifty per cent, of recent 

 fossils. 



OLE'CRANOBT. (o\eicpavov, Gr. from 

 u>\wrj t the ulna, and Kapyvov, the 

 head.) A process of one of the 

 bones of the fore arm, the ulna, 

 forming part of the elbow joint. 



OLE'FIANT GAS. (from oleum, oil, and 

 fio, to become, Lat.) A gas devoid 

 of colour and taste, deriving its 

 name from the property it possesses 

 of forming an oil-like liquid with 

 chlorine. 



O'LIQOCLASE. Soda Spodumene. A 

 feldspathic mineral, whose const!- 



