﻿J. 8. Gardner — Cretaceous DentaUadce. 371 



Phillipsite or lime Harmotome also occurs, associated with, the pre- 

 ceding, just as in the amygdaloidal trap of Iceland. In hollows of 

 the calcareous cement small crystals of apophyllite occur, with pul- 

 verulent and minutely crystalline fluor spar, together with other 

 minerals not identified, but resembling in character gismondine and 

 scolezite. At Plombieres hyalite occurs with the zeolites ; and where 

 the masonry is exposed to the full flow of the water there is a trans- 

 parent gelatinous deposit, which becomes white and opaque when 

 dry, and is a hydrated silicate of lime analogous to okenite. Aragon- 

 ite occurs generally in acicular crystals, but sometimes of the form 

 called apotcme by Haiiy, found in iron ore deposits and in some 

 basalts. Calcite is frequently associated with the ch-abasite, as in 

 Icelandic lavas> Halloysite is also met with at Plombieres-. 



Besides the formation of geodes in' the visible cavities, the whole 

 substance of the bricks was found to be altered by contact with the 

 water. This change rendered the originally friable brick very hard 

 and compact ; and microscopic examination showed that its minute 

 pores- were fi.lled with colourless and transparent mineral substances. 

 The author gaA^e the following list of the minerals thus found : — 

 Chabasite, christianite (?), mesotype, hyalite (?), tridymite, chalce- 

 dony in radiate spherules, calcite, and some globular bodies of un- 

 certain nature. The association of chalcedonic quartz with opal is 

 interesting, as proving that silica may be deposited in the anhydrous 

 form when the temperature of the surrounding medium does not 

 exceed 70*^ C. Analysis showed that the amou-nt of zeolitic substance 

 added to the bricks is from 13 to 14 per cent, of the total weight. 



This contemporary production of zeolites and other minerals 

 identical with those found in amygdaloidal and many other altered 

 volcanic rocks is regarded by the author as an experimental demon- 

 stration of the mode of formation of the latter, which are no doubt 

 produced in a similar manner by the percolation of water through 

 the substance of the rocks, conveying to, and depositing in, their 

 cavities mineral substances, dissolved during its passage. Zeolitic 

 minerals, as he says, may therefore be considered a kind of " ex- 

 tract " of the rocks so subjected to continued lixiviation. And the 

 process being effected independently of any peculiar conditions of 

 heat and pressure, would seem to show that no such conditions are 

 essential in the production of natural zeolites. 



6. "On the Cretaceous Dentaliadse." By J. S. Gardner, Esq., 

 F.G.S. 



In this paper the author described the Dentaliadse from the British 

 Cretaceous rocks, of which he enumerated the following species : — 

 Dentalium decussatum, Sow., and var. ellipticum, Sow. (Gault) ; D, 

 medium, Sow, (Gault, Greensand, and Grey Chalk) ; D. divisiensis, 

 sp. n. (Upper Greensand) ; D. alatum, sp. n. (Gault) ; D. cylindricum, 

 Sow. (Blackdown) ; D, acuminatum, sp. n. (Gault) ; D. suhtetrago- 

 num, sp. n. (Gault) ; D. tetrngonum, sp. n. (Gault) ; Enialis Meyeri, 

 sp. n. (Blackdown) ; and Gadus gaultinus, sp. n. (Gault).. 



7. •'' On a number of New Sections around the Estuary of the 

 Dee which exhibit Phenomena having an Important Bearing on the 



