80 REPORT—1850. 
and Dr. Mantell. With the exception of certain vertebrata (reptiles and fishes), we 
owe to Dr. Fitton our information respecting the fauna. No minute investigation 
of the strata, in connexion with their organic contents, had, however, been under- 
taken, nor had the latter been collected to any extent, as may be seen when the pub- 
lished lists, including about twelve species of Mollusca and Crustacea from these 
beds, are compared with those now submitted to the Section, in which more than 
seventy members of those classes are enumerated. This increased catalogue is not 
merely of value on account of the great numbers of species, it is remarkable on ac- 
count of the new and interesting light it throws on the distribution of freshwater 
creatures during the oolitic period. 
The points at which these observations were made were Lulworth Cove and the 
neighbouring bays, Warbarrow Bay, (on one side of which, at Meup’s Bay, is the 
clearest and most complete of all the Purbeck sections,) Osmington, Upway and 
Ridgeway, between Weymouth and Dorchester, and Durlestone Bay, near Swanage. 
Subsequently the base of the Purbecks exposed in the great Portland quarries at 
Swindon, a section which had previously been examined and accurately described 
by the Rev. P. B. Brodie, was visited, and found to correspond exactly in mineral 
characters and organic contents with the beds at the base of the Purbecks in Dor- 
setshire. From all these localities ample collections were made, in which the author 
had the assistance, for several months, of Mr. J. Gapper, of the Geological Survey. 
The results of these researches, whether new or confirmatory of older observations, 
may be stated briefly as follows :— 
Ist. There is no passage from the Portlands into the Purbecks. The top beds of 
the Portland stone are purely marine: the lowermost beds of the Purbeck are purely 
freshwater, containing Cyprides, Valvata and Limneus. At Meup’s Bay, these lowest 
freshwater beds, forming the “ cap,” occupy a thickness of a little more than eight 
feet, and are surmounted by the great dirt-bed, containing the stools of Cycadee. 
A little above this dirt-bed is a second, less developed, and a similar one occurs in 
many places below it. 
Above the highest dirt-bed, the Cypridiferous shales which follow are strangely 
contorted and broken up in all the sections at the west end of the Isle of Purbeck. 
These are capped by undisturbed beds full of Cyprides, succeeded by twenty feet 
or more of shales, calcareous slates, marls and limestones, with occasionally siliceous 
bands, all for the most part deposited in brackish water, and filled, in many places, 
with Rissoe of the subgenus Hydrobia, and a little Cardium of the subgenus Profo- 
cardium. 
Many of these beds abound in a species of Serpula, closely allied to, if not identical 
with, Serpula coacervites of the German Purbecks. There are above thirty feet of 
these brackish water-beds at Meup’s Bay. They are capped by purely freshwater 
marls, containing the same species of Cypris, Valvata and Limneus, as occur in the 
lowest beds of the Purbecks. 
Suddenly, without any disturbance, a change takes place. A very thin band of 
greenish shales, full of impressions of leaves like those of a large Zostera, and with 
traces of marine shells, cuts off the freshwater strata. Immediately, however, new 
freshwater beds succeed, filled in many places with fossils, species of Cypris, Valvata, 
Paludina, Planorbis, Limneus, Physa and Cyclas, all different from any we had pre- 
viously seen in the Jower beds. Thick bands of cherty stone, filled with these fossils 
in a beautiful state of preservation, occur, and among them are for the first time in 
the oolitic series, Gyrogonites, the spore vesicles of Char@. Immediately above these 
interesting bands (in which many remains of fish were also found) is the great and 
conspicuous stratum long familiar to geologists under the local name of “ Cinder-bed,”” 
formed of a vast accumulation of Ostrea distorta shells. In this bed the author dis- 
covered the first Echinoderm ever seen in the Purbecks. It proved to bea species of 
Hemicidaris, a genus characteristic of the oolitic period ; it was accompanied by a 
species of Perna. The cinder-bed is succeeded by limestones and shales, partly of 
fresh water and partly of brackish origin. In these the same species of Cypris 
occur which mark the shaly bands near the chert below the cinder. Many fish, 
especially species of Lepidotus and Microdon radiatus, are found in these bands ; and 
in the fine collection of Mr. Wilcox of Swanage, are the heads of two magnificent 
species of the reptile Macrorhynchus, from this horizon in the Purbecks. Among the 
