Upper 

 Galleey. 



Wall-case 40 



34 CALCAREOUS TUFAS, ETC. 



27. — Calcareous tufa encrusting stems of plants. — From 

 the Great Northern Railway. Presented by Thomas Rey- 

 nolds, Esq. 



28. — Calcareous tufa, encasing plants. 



29. — Calcareous tufa 



Yorkshire. 

 30. 



encasing 



plants. 



Richmond, 



Wi 



the fi 



o 



concentric concretions of lime with numerous land and 

 freshwater shells of existing species. 



See " Survey Memoir on the Fluvio -marine strata of the 



31. — Calcareous tufa, deposited 



Map 



Carbonift 



limestone by old springs now dried, and containing stems 



>/ 



with land shells. — Near 



De 



The tufaceous deposits from 25 to 31 are all compara- 

 tively recent, and enclose plants and shells of living species. 



32. — Tufaceous limestone, from the 



Portland 



Map 



" cap " beds of 



Hospital Quarry, Isle of Portland. 



In the Isle of Portland, interposed between the slaty 

 limestone of the Purbeck and the true Portland stone there 

 is a series of " dirt beds " and beds of hard irregular lime- 

 stone, termed by the quarrymen " caps," from the positions 

 occupied by them in reference to the latter. The thickness 

 of these beds is very variable ; even at short intervals, 

 and in the same/quarry, the upper bed, called " top cap," 

 varies from four feet to four feet six inches in thickness ; 

 and the lower, or " skull cap," from six inches to four feet 

 and more, A "dirt bed" frequently divides the " skull cap 

 from the Portland stone. The caps are hard tufaceous 

 limestones, constituting, strictly speaking, the base of the 

 lower Purbeck beds ; and the late Professor Forbes, adopting 

 this view in his classification of that group, retained the 

 trivial name, as expressive of their mode of occurrence, 



designating them " soft " and " hard " cap respectively. 



J> 



P 



It 



curren 



26.- 



tlr 



them 



fi 



tii 



ofWHI 



masses 



used f 

 No. 16 



41, 



rented 



42,- 



43, 



44, 



; er 



an 

 l! Tl 



