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O O L 



heavy rain ; they are of a rounded form, 

 and have been compared to turbans. 



OME'NTUM. (omentitm, Lat.) The caul. 



OMNI'VOROUS. (from omnis, all, and voro, 

 to devour, Lat.) Animals which eat food 

 of all kinds. 



O'MOPLATE. (from w/*og, the shoulder, 

 and TrXarrg, broad, Gr.) The scapula, 

 or shoulder-blade. 



O'NCHUS. A genus of sharks, belonging to 

 the sub-family of Hybodonts, teeth of 

 which have been found in the lias, at 

 Lyme Regis. 



O'OLITE. (from MOV, an egg, and XiOog, a 

 stone, Gr. oolites, Fr.) A group of 

 strata, whose order of superposition is 

 below the Purbeck and above the lias : 

 called also the Jura limestone. The two 

 lowest members of this group, or those 

 immediately above the lias, are called the 

 great oolite, and the inferior oolite. All 

 the members of the group are marine 

 deposites. The oolite has been thus named 

 from its being composed of spherical gra- 

 nular concretions, supposed to resemble 

 the roe, or eggs, of a fish : it is a mere 

 term of convenience, like those of carbo- 

 niferous, red-sandstone, &c., for many 

 limestones in other groups are oolitic. 

 The oolite is an accumulation of sands, 

 sandstones, marls, clays, and limestones. 

 A very striking zoological feature of this 

 group is the immense abundance of am- 

 monites and belemnites which must have 

 existed previous to, and during, its de- 

 posit ; for, notwithstanding the usual 

 chances of destruction to which we may 

 suppose they were exposed, myriads of 

 their shells have been found entombed 

 entire, and not unfrequently the animal 

 must have been in them. One hundred 

 and seventy-three species of ammonites, 

 and sixty-five species of belemnites have 

 been enumerated as discovered in the 

 oolite. There can be little doubt that 

 this group, greatly expanded in thickness, 

 and mixed with sandstones, marls, and 

 slates, possessing a very different aspect 

 from the equivalent rocks in a large por- 

 tion of Western Europe, extends over 

 various parts of Eastern Europe. At 

 present it seems to be considered that 

 rocks equivalent to the oolitic group have 

 not been detected in North America. 

 The aggregate average thickness of the 

 oolite may be estimated at 1200 feet. In 

 some instances the spherical granular 

 concretions, which are imbedded in many 

 of the strata, attain the size of a pea, and 

 this variety has obtained the name of 

 pisiform oolite. Some oolites have been 

 used for building-stone, but they are said 

 not to be durable. Somerset House is 

 built of oolite. The vertebrated animals, 

 whose remains are found in oolite, are 



fishes and reptiles of the same genera as 

 those discovered in the lias. Some strata 

 of this group are composed, almost en- 

 tirely, of madreporites, and these have 

 been called " coral ragg." Other strata 

 abound in the remains of fossil alcyonia 

 and sponges, and with congeries of minute 

 millepores and madrepores. In England, 

 the limestone of the oolite has a yellow- 

 ish brown, or ochreous colour, by which 

 it may at once be distinguished from the 

 lias ; and the fossils partaking of the 

 colour of the limestone, renders it easy 

 to separate them from the fossils of the 

 lias. The oolite has been divided into 

 three formations, the upper, the middle, 

 and the lower. Between the lower and 

 the middle division of oolites, there oc- 

 curs a bed of dark blue clay, called Ox- 

 ford, or clunch, clay, the thickness of 

 which has been stated to be 200 feet. 

 Between the middle and upper also, there 

 is found a thick bed of clay, called Kim- 

 meridge clay, of a thickness exceeding, 

 in some parts, 100 feet. The uppermost 

 members of the oolite group are the 

 Portland beds, lying immediately under 

 the Purbeck beds. 



Ooolite has been also called roe-stone, 

 from a supposition of the older geologists, 

 that the globules contained in it were the 

 petrified roes of fishes. In the litho- 

 graphic limestone of Solenhofen, belong- 

 ing to one of the upper members of the 

 oolite, a great variety of organic remains 

 is found ; and in the museum of Count 

 Munster, there are not fewer than seven 

 species of flying lizards, six saurians, 

 three tortoises, sixty species of fishes, 

 forty-six species of Crustacea, and twenty- 

 six species of insects, taken from that 

 deposit. 



The lower division of the oolite in York- 

 shire, and in Scotland, contains coal for- 

 mations. In the district north of the 

 river Humber, the lower oolite assumes a 

 new character : instead of finding beneath 

 the cornbrash the forest marble and great 

 oolitic beds of sandstone, shale and car- 

 bonaceous matter are interpolated above 

 the sand which covers the lias. Proceed- 

 ing northwards, these strata rapidly in- 

 crease in thickness, and the carbonaceous 

 layers gradually become concentrated 

 into a stratum of coal, which, though 

 never exceeding sixteen inches in thick- 

 ness, is, from local circumstances, of con- 

 siderable value. 



The oolitic tracts of England present a 

 broad band of dry limestone surface, 

 rising westward to elevations of from 800 

 to 1,400 feet, with escarpments com- 

 manding very extensive prospects over 

 the undulating plains of lias and red 

 marl. The whole tortuous line of oolitic 



