LUDLOW GROUP

ludlow group, or ludlovian, in geology, the uppermost subdivision of the silurian rocks in great britain. this group contains the following formations in descending order:--tilestones, downton castle sandstones (90 ft.), ledbury shales (270 ft.), upper ludlow rocks (140 ft.), aymestry limestone (up to 40 ft.), lower ludlow rocks (350 to 780 ft.). the ludlow group is essentially shaly in character, except towards the top, where the beds become more sandy and pass gradually into the base of the old red sandstone. the aymestry limestone, which is irregular in thickness, is sometimes absent, and where the underlying wenlock limestones are absent the shales of the ludlow group graduate downwards into the wenlock shales. the group is typically developed between ludlow and aymestry, and it occurs also in the detached silurian areas between dudley and the mouth of the severn. the _lower ludlow rocks_ are mainly grey, greenish and brown mudstones and sandy and calcareous shales. they contain an abundance of fossils. the series has been zoned by means of the graptolites by e. m. r. wood; the following in ascending order, are the zonal forms: _monograptus vulgaris_, _m. nilssoni_, _m. scanicus_, _m. tumescens_ and _m. leintwardinensis_. _cyathaspis ludensis_, the earliest british vertebrate fossil, was found in these rocks at leintwardine in shropshire, a noted fossil locality. trilobites are numerous (_phacops caudatus_, _lichas anglicus_, _homolonotus delphinocephalus_, _calymene blumenbachii_); brachiopods (_leptaena rhomboidalis_, _rhynchonella wilsoni_, _atrypa reticularis_), pelecypods (_cardiola interrupta_, _ctenodonta sulcata_) and gasteropods and cephalopods (many species of _orthoceras_ and also _gomphoceras_, _trochoceras_) are well represented. other fossils are _ceratiocaris_, _pterygotus_, _protaster_, _palaeocoma_ and _palaeodiscus_. the _upper ludlow rocks_ are mainly soft mudstones and shales with some harder sandy beds capable of being worked as building-stones. these sandy beds are often found covered with ripple-marks and annelid tracks; one of the uppermost sandy layers is known as the "fucoid bed" from the abundance of the seaweed-like impressions it bears. at the top of this sub-group, near ludlow, a brown layer occurs, from a quarter of an inch to 4 in. in thickness, full of the fragmentary remains of fish associated with those of _pterygotus_ and mollusca. this layer, known as the "ludlow bone bed," has been traced over a very large area (see bone bed). the common fossils include plants (_actinophyllum_, _chondrites_), ostracods, phyllocarids, eurypterids, trilobites (less common than in the older groups), numerous brachiopods (_lingula minima_, _chonetes striatella_), gasteropods, pelecypods and cephalopods (_orthoceras bullatum_). fish include _cephalaspis_, _cyathaspis_, _auchenaspis_. the tilestones, downton castle sandstone and ledbury shales are occasionally grouped together under the term _downtonian_. they are in reality passage beds between the silurian and old red sandstone, and were originally placed in the latter system by sir r. i. murchison. they are mostly grey, yellow or red micaceous, shaly sandstones. _lingula cornea_, _platyschisma helicites_ and numerous phyllocarids and ostracods occur among the fossils. in denbighshire and merionethshire the upper portion of the denbighshire grits belongs to this horizon: viz. those from below upwards, the nantglyn flags, the upper grit beds, the _monograptus leintwardinensis_ beds and the dinas bran beds. in the silurian area of the lake district the coldwell beds, forming the upper part of the coniston flags, are the equivalents of the lower ludlow; they are succeeded by the coniston grits (4000 ft.), the bannisdale slates (5200 ft.) and the kirkby moor flags (2000 ft.). in the silurian areas of southern scotland, the ludlow rocks are represented in the kirkcudbright shore and riccarton district by the raeberry castle beds and balmae grits (500-750 ft.). in the northern belt--lanarkshire and the pentland hills--the lower portion (or ludlovian) consists of mudstones, flaggy shales and greywackes; but the upper (or downtonian) part is made up principally of thick red and yellow sandstones and conglomerates with green mudstones. the ludlow rocks of ireland include the "salrock beds" of county galway and the "croagmarhin beds" of dingle promontory. see silurian, and, for recent papers, the _q. j. geol. soc._ (london) and _geological literature_ (geol. soc., london) annual. ludolf (or leutholf), hiob (1624-1704), german orientalist, was born at erfurt on the 15th of june 1624. after studying philology at the erfurt academy and at leiden, he travelled in order to increase his linguistic knowledge. while in italy he became acquainted with one gregorius, an abyssinian scholar, and acquired from him an intimate knowledge of the ethiopian language. in 1652 he entered the service of the duke of saxe-gotha, in which he continued until 1678, when he retired to frankfort-on-main. in 1683 he visited england to promote a cherished scheme for establishing trade with abyssinia, but his efforts were unsuccessful, chiefly through the bigotry of the authorities of the abyssinian church. returning to frankfort in 1684, he gave himself wholly to literary work, which he continued almost to his death on the 8th of april 1704. in 1690 he was appointed president of the _collegium imperiale historicum_. the works of ludolf, who is said to have been acquainted with twenty-five languages, include _sciagraphia historiae aethiopicae_ (jena, 1676); and the _historia aethiopica_ (frankfort, 1681), which has been translated into english, french and dutch, and which was supplemented by a _commentarius_ (1691) and by _appendices_ (1693-1694). among his other works are: _grammatica linguae amharicae_ (frankfort, 1698); _lexicon amharico-latinum_ (frankfort, 1698); _lexicon aethiopico-latinum_ (frankfort, 1699); and _grammatica aethiopica_ (london, 1661, and frankfort, 1702). in his _grammatik der athiopischen sprache_ (1857) august dillmann throws doubt on the story of ludolf's intimacy with gregorius. see c. juncker, _commentarius de vita et scriptis jobi ludolfi_ (frankfort, 1710); l. diestel, _geschichte des alten testaments in der christlichen kirche_ (jena, 1868); and j. flemming, "hiob ludolf," in the _beitrage zur assyriologie_ (leipzig, 1890-1891).