LOWER LIAS ower sh i ' Bone bed . GOO " The upper lias consists of thin limestone beds scattered through a great thickness of blue clay, more or less indurated, and so aluminous that it has been wrought for alum at Whitby. A thick band of vegetable matter or impure lignite occurs in this division, in which are found nodules and lumps of jet, a peculiar mineral composed of carbon and hydrogen, and probably having a similar origin to the amber of the tertiary ]ignites. A series of brown and yellow sands, and a peculiar layer called the cephalopodf bed, from the abundance of these fossils contained in it, occur above these clays; recently, they have been separated from the inferior oolite, and joined to this division, on the evidence of the contained fossils.
The marlstone is an arenaceous deposit, bound together either by a calcareous or fer ruginous cement, in the one case passing into a coarse sltelly limestone, and in the other into an ironstone, which has been extensively wrought both in the north and south of England.
The lower lias beds consist of an extensive thickness of blue clays, intermingled with layers of argillaceous limestone. In weathering, the thin beds of blue or gray limestone become light brown; while the inter-stratified shales retain their dark color, giving the quarries of this rock, at a distance, a striped or ribbon-like appearance, whence, it is sup posed, the miner's name lias or layers is derived. Generally the clays rest on triassic rocks, but occasionally there is interposed a thin bed of limestone, containing fragments of the bones and teeth of reptiles and fish, generally of undoubted liassie age; occasion ally, the bones of keuper reptiles are met with in it, causing it to have been referred to the trias.
The lias is highly fossiliferous, the contained organisms being well preserved; the fishes are often so perfect as to exhibit the complete form of the animal, with the fins and scales in their natural position. Numerous remains of plants occur in the lignite and in the shales. The name gryphite limestone has been given to the lias, from the great quantities of gryphea incurvala , a kind of oyster, found in it. Some of the older genera of mollusca are still found in these beds, but the general character of these animals more nearly approaches the newer secondary forms. Fish remains are frequently met with ; the reptiles, however, arc the most striking features. They are remarkable for the great numbers in which they occur, for the size which many of the species attain, and for the adaptations in their structure which fitted them to live In water. The most noteworthy are species of ichthyosaurus (q.v.) and plesiosaurus (q.v.).
The Hassle rocks extend in a belt of varying breadth across England, from Whitby, on the coast of Yorkshire, s. to Leicester, then s.e. by Gloucester, to Lyme Regis in Dor. setshire.