File:The Quarterly journal of the Geological Society of London (13960642273).jpg

FEOM R THE EADIOLAEIAST MAELS OF BAEBADOS.

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the tests are flexible, composed of hexagonal plates, provided with

apetaloid ambulacra, with a single pore in each plate of the ambu-

lucra, and an epistroma of minute granulation with small sparsely

scattered tubercles exactly like those of some of the Pcrischoechinidae,

such as Palcecliinus. This is not the time to discuss the meaning of

these resemblances, but they are too striking to be wholly ignored.

As

 Cystecliinus crassus adds but little to our knowledge of the 
 

morphology of the genus, the chief interest of the specimen depends

on the place of its occurrence and on the light it throws upon the

age and origin of the classical Eadiolarian deposits of Barbados

and some questions connected therewith.

The Island of Barbados is composed of three distinct sets of beds

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the Scotland formation ; the Eadiolarian deposits ; and the Coralline

limestone. The term Scotland formation was applied by Sir E.

Schomburgk * to the beds in the island below the Coralline lime-

stone, and including the Eadiolarian deposits ; but as we are informed

by Mr. J ukes-Browne and Prof. Harrison f that they will shortly be

able to prove that the latter are quite distinct and over lie the other

un conformably, the term may be restricted to the lower beds. As

such it would include a group of strata which Sir E. Schomburgk

describes J as composed " of siliceous sandstone, intermixed with ferruginous matter, calcareous sandstones, siliceous limestones, different kinds of clay, selenite, and earthy marls, frequently containing

fragments of pumice, strata of volcanic ashes, seams of bitumen, and

springs of petroleum (Barbados tar)." The rocks of this formation

appear to form the whole substructure of the island, though they

only appear through the capping of coral limestone over one seventh

of the total area. Their age has, unfortunately, never been conclu-

sively settled. Three new species were found in these beds by Sir

E. Schomburgk and described by Porbes § ; the species were as follows :

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(1) Scalaria Ehrenhergi, Pbs., found in the siliceous limestone of

Bissex hill. Though Porbes remarked the close resemblance of this

specimen to the S. crassilabrum, Sow., of the Philippines and Central

America, he considered it as probably of Miocene age.

(2) Nucula Packeri, Pbs. Allied to some tropical, subtropical,

and Crag forms.

(3) Nucula ScliomburgTci, Pbs. A species attributed to a small

section of the genus, which ranges from the Cretaceous upwards,

but of which the nearest ally is probably Nucula Cobholdiaz of the

Crag.

So far as I am aware this is the only direct palseontological evidence,

except for the Eadiolaria, as to the age of the beds, and it was upon