DIVISIONS OF THE LIAS. 361 its rich iron deposit surrounding each area (except Rosedale), succeeded by the Upper Lias and estuarine or Moor group. It is meteoric and river denudation alone which has revealed in these central dales and becks the corresponding features of the Upleatham, Eston, and Cleveland deposits of iron ores, &c. The chief development of the Liassic deposits are, therefore, best seen and understood in the North Riding ; that the Lias is continuous, under the covering of the estuarine Oolites and Chalk to the Humber, cannot be doubted, though only the Lower beds are clearly seen, the Upper being covered or only occasionally exposed. South of Market Weigh ton, at Cliff, Hotham, and Cave, and on to Brough, the Lowest Lias is exposed—though not greatly developed ; the Inferior Oolite of the Lincolnshire type occurs at South Cave, 1 and is continued across the Humber, there becoming greatly expanded, and extending into Lincolnshire and Northamptonshire. TABLE LIL—Divisions or Stages of the Lias as adopted by cCOrbigny and French, Authors. UPPER Lias. 4 TOARCIEN (so named from Thouars = Upper Lias) in France composed of alternations of limestone and clays ; in Eng land clays, shales, and sands ; may be separated palonto- logically into an upper series (clays and sands), containing Ammonites oprdinus. A.Thouarsensis. A. radians. A.insignis. and A. variabilis—all present in the Upper Lias of Eng land. A middle series with Am. bifrons. and a lower series with Am. sei-pentinus and A. complanatus occur. (3- Middle Lias. < I 2. Loweb Lias. / i. \ LIASSIEN (= Middle Lias)—composed of marls and argil laceous and sandy limestones ; divisible into 3, if not 4 zones, as in the Middle Lias of England. Zone 1, Am. Margaritatus; zone 2, Am. spinatus; zone 3, Am. Davcei; zone 4, Am. Jamesoni. SINMURIEN (= Lower Lias) — composed of argillaceous limestones and marls, and divided into the normal series of Ammonite zones—in England 7 (see Lower Lias, p. 362). HETTANGIEN (Infra-Lias) — marly and shelly limestones, with Am. planorbis, corresponding to our Angulatus and Planorbis zones at the base of the Lias, resting conformably upon the sandstones, marls, and bone bed of the Avicula contoi’ta or Rhaetic series. Life Zones.—This division of the Lias into three stages is now acknowledged throughout Europe; and these three are again sub divided into beds or zones which are characterised by certain species of Ammonites. 2 The Lower Lias is clearly divisible by its fossils into seven well- defined horizons or zones characterised by certain species of Ammonites. Reading upwards, they are as follows :— 1 The Cave Oolite of Phillips. 2 The Lower Lias into 7 zones ; the Middle into 6 zones ; and the Upper Lias into IO or II zones.