THE PORTLAND BUILDING STONE. 
211 
sent the building stone ; almost all is chalky, and at the base 
flint-bearing. All along the coast from St. Alban’s Head to 
Swanage one part or other of the series is found ; but though 
the representatives of the upper stone may be recognized by 
a geologist, their value is obviously comparatively small. At 
the coast south of Worth-Maltravers, and at Tillym, stone is 
extracted, but it is obtained from a distinct bed, developed 
at a lower level than the White bed, and scarcely represented 
in the island. It is a very good freestone, white,, and of fine 
grain, but large blocks have to he mined for. 
These are the whole of the English localities where ‘ Port- 
land Stone ’ is quarried, but the same rocks yield an abundant 
supply in the neighbourhood of Boulogne. Some of the stone 
here worked belongs undoubtedly to the same horizon as the 
lower beds at Portland, but the great quarries of Mont Lambert 
and Chatillon are said by the French geologists to belong to an 
earlier episode. Dr. Fitton was of a different opinion, and a 
hasty examination of them leads me rather to coincide with 
him in this. The similarity of the rocks to those at Swindon 
is remarkable in the extreme. 
Such are the Portland building stones. One very remarkable 
feature about them is that they are not as a rule oolitic. Beds 
of very clean oolite do occur among them, consisting of the 
little rounded grains alone, with scarcely a particle of visible 
cement, but those that are of value have seldom any of these 
grains ; they consist rather of exceedingly fine fragments, when 
any structure can be made out, derived from shells and other 
organisms. This peculiarity has been noticed by Mr. Sorby in 
his anniversary address to the Geological Society for 1879, and 
a remarkable addition made by a study of the microscopic 
structure. He states that the most abundant fragments are of 
Echinoderms, Brachiopoda, Ostrese, Polyzoa, and Aviculae. 
Now except the oyster itself, rarely associated with the actual 
building stone, all the others are exactly the classes of organisms 
which can seldom or never be found in the rocks. Echinoderms 
are of excessive rarity, while no one has ever seen to my 
knowledge a single Brachiopod, Polyzoan, or Avicula in the 
Portland limestone. The absence of Brachiopods especially is 
remarkable, though certainly they were not abundant in the 
Corallian limestones, yet in most limestones they are numerous. 
Did they exist and become universally ground to powder P or are 
the fragments of shells not those of animals living at the time, 
but derived from older rocks ? If the Kimmeridge Clay were 
derived from the Lias, the Portland Stone might well be derived 
from the Bath Oolites. There is a singular absence, too, of 
corals ; the accompanying absence of oolite lends strong support 
to the view that these two are intimately connected. These 
