98 THE LIAS AMMONITES. 



Sandy shales, impure limestone bands, grey marly sandstone, blue micaceous 

 sandstone; about ten feet thick, containing Protocardium truncatum, Pecten (squivalvis, 

 Pelemnites virgatus. 



My friend Professor Judd, in his able and exhaustive ' Memoir on the Geology of 

 Rutland,' gives the following account of the Marlstone or Middle Lias in that county. 

 " The upper part is a mass of ferruginous limestone, known as the Rock-bed ; the lower, a 

 series of sandy and micaceous clays and iron-stone with some beds of sand. The succession 

 of beds in the Marlstone is as follows in ascending order, beginning at the base : 



" a. Soft, yellowish-brown, sandy, and micaceous ironstone, crowded with casts of shells 

 and alternating with light blue clays. These ferruginous bands vary very greatly in 

 number and thickness, and are sometimes nodular. They are especially characterised 

 by the abundance of several small varieties of Ammonites margaritatus, Montf., and 

 Protocardium truncatum. Sow. 



" b. Beds of blue, highly micaceous clay, with large septaria crowded with fossils." 

 Only in two brick-yards. "The most abundant species in these beds are Ammoiiites 

 margaritatus, Mont, (the large typical form), Belemnites elongatus Mill., Cryptcsnia 

 expansa, ^aw.,Avicula in<sqmvalvis. Sow., MgtilusMjjpocamjJus, Young and ^ivd,Modiola 

 scalprum. Sow. (very abundant), Protocardium truncatum. Sow., Pleuromya unioides, 

 Rom., and Pentacrinus subangularis. Mill. 



" c. Beds of blue clay, with septaria, the latter not unfrequently containing Specular 

 Iron, and weathering to a red colour. They contain many of the fossils recorded from 

 the preceding beds, but less abundantly . . . . . . 



" d. Light blue clays, with bands of ir onstone balls of concentric structure, and usually 

 very unfossiliferous. These beds are exposed in some brick-yards." At some places 

 they contain beds of green and brown sands, as near Horninghold. 



" e. ' The Rock-bed.' This is a mass of Hmestone, more or less ferruginous, and 

 occasionally passing into a good ironstone. When unweathered it is a hard crystalline 

 rock, of a blue or green colour, but as usually seen it is brown and moderately soft. It 

 is usually crowded with fossils, its mass being often made up of fragments of crinoids, 

 spines of Echinoderms, Serpulge, and fragments of shells, whilst certain beds in it consist 

 of an agglomeration of shells of Phjnchonella teirahedra. Sow., and Terebratula punctata. 

 Sow., often filled with finely crystallized calc-spar. Belemnites paxillosus, Schloth., 

 and B. elongatus. Mill., are extremely abundant in the Marlstone Rock-bed, and serve to 

 distinguish it from the Northampton Sand, which often resembles it in mineralogical 

 characters, but in which Belemnites are exceedingly rare. Ammonites are not abundant 

 in the Rock-bed in this district, but at some points, as Edmondthorpe, Loddington, 

 and Horninghold, Ammonites communis, Sow., and Am. annulatus. Sow., occur in consider- 

 able numbers ; Am. spinatus, Brug., and some varieties of Am. margaritatus, Montf., are 

 also fo'.xnd in it, but much more rarely, in this district. Large specimens of Peclen 

 ^ "The Geology of Rutland," ' Memoirs of the Geological Survey,' p. 64, 18/5. 



