423 



THE GEOLOGIST, 



incurva in profuse abundance; an occasional thick cast of Homomyay 

 and Cardinia Lister i, with its varieties hjlrida and imhricata ; all these 

 often imbedded in fox-coloured ragstones of indurated clay ; then Lima 

 gigantea, in bright and beautiful specimens, exceedingly prevailing in 

 the bands of limestone ; Lima antig^uata, Pentacrinus tuherculatus, Pinna 

 folium, Pecten, Avicula ; two species of Ammonites, in the state of broken 

 and undefinable casts ; a Unicardiiim, a large oval Cardinia, fragments 

 of wood, microscopic round- mouthed Terebrm, spines of sea-urchins, 

 masses of Vermetus ; a single Caryophjllia f? J, Ostrea minima f syn. 

 Liassica), Modiola minima, and a larger species, and slabs extremely 

 crowded with the larger Posidonomya (so called by the late Mr. Strick- 

 land), which is here found associated with the small Modiola and 

 Cardium that accompany it in the south. The Posidonomya-hed''^ can 

 be better examined at Hotham than at any other place with which I am 

 acquainted. About Coombe Hill, in Gloucestershire, this fossil may 

 occasionally be found lying on tlie ploughed lands, but chiefly as a cast, 

 and in a bouldered state, whereas, at Hotham, it occurs in dense layers, 

 and in every state of growth, imbedded in a very fine-grained, dark-blue 

 stone, of a whitish colour externally, the sections of which exhibit lines 

 indicative, sometimes, of a very gently rippled, and, sometimes, a most 

 peaceful lamination. This bed makes excellent roadstone, being 

 very hard and intractable, and splitting rather vertically than in the 

 direction of its deposit. The dense layers seldom contain any 

 other shell besides the Posidonomya, though there is, at times, 

 an admixture, in subordinate numbers, of the characteristic Cardium 

 and Modiola of Gloucestershire. One slab in my possession, not two 

 inches thick, is exclusively occupied on one side with Posidonomya, 

 and on the other with the Cardium and Modiola. The former of 

 these shells is very difficult to be detached from its matrix in a 

 perfect state. Portions of it may be obtained for microscopic 

 examination, but as yet I have never seen the hinge. 



I was deceived by this stratum into the expectation that I might, 

 perhaps, find the "Bone-bed," and Insect-bed " in this range at 

 Hotham. The Lowest Lias may be seen in the marl-pits, passing con- 

 formably into jSTew Eed Sandstone, by alternating layers of Lias and 

 sand disposed horizontally in slightly-wavy lines. This transition is 

 apparently abrupt and sudden, and is completed in a very few feet, so 

 that wc have beds of fine,, rod-coloured sand hastily exchanged for 



