J. S. Gardner — Cretaceous Dentaliadce. 
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 ci'ystalline 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 apotome by Haüy, found in iron ore deposits and in some 
basalts. Calcite is frequently associated with the chabasite, 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 filled with colourless and transparent mineral substances. 
The autlior gave the following list of the minerals thus found : — 
Chabasite, christianite (?), mesotype, hyalite (?), tridymite, clialce- 
dony in radiate spherules, calcite, and some globular bodies of un- 
cei'tain nature. The association of chalcedonic quartz with opal is 
interesting, as proving that silica may be deposited in the anhydrous 
form wlien the temperature of the surrounding medium does not 
exceed 70° C. Analysis showed that the amount 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 sliow that no such conditions are 
essential in the production of natural zeolites. 
6. “ On the Cretaceous Dentaliadae. 1 ’ By J. S. Gardner, Esq., 
F.G.S. 
In this paper the author described the Dentaliadxe from the British 
Cretaceous rocks, of which he enumerated the following species : — 
Dentalium decussahm, Sow., and var. ellipticum, Sow. (Gault) ; J). 
medium, Sow. (Gault, Greensand, and Grey Chalk) ; D. divisiensis, 
sp. n. (Upper Greensand) ; D. alatum, sp. n. (Gault) ; D. cylindncurn, 
Sow. (Blackdown) ; D, acuminatum, sp. n. (Gault) ; D. subtetrago- 
num, sp. n. (Gault) ; D. tetrngonum, sp. n. (Gault) ; Entalis Meyeri, 
sp. n. (Blackdown) ; and Gadus gaultinm, 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 
