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POPULAR SCIENCE REVIEW. 
observations on its structure lead to the conclusion that a large 
proportion at least of Portland Stone is derived not directly 
from broken-down shells forming calcareous mud, and subse- 
quently consolidated, but from previously formed shelly lime- 
stones, either nearly contemporaneous or more remote in time. 
At all events, the name ‘ Portland Oolite ’ is to a great extent 
a misnomer, and for some of the rocks which are worked as 
building stones, ‘ Portland Limestone ’ is not much better. The 
great value of the stones is derived from their being so finely 
and uniformly ground, while their calcareous cement gives 
them the quality of many limestones of being easily worked, 
and these advantages are shared, though in a minor degree, 
by the beds at Worth, the Yale of Wardour, and Swindon. 
