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POPULAR SCIENCE REVIEW. 
town, and in a small outlier at B our ton. But the great 
quarries at Swindon itself, yielding a stone of considerable 
importance and which has been very largely worked for houses 
and churches in the district, belong to a higher part of the 
series ; in fact, they are seen overlying the other. Tiie stone 
here occurs in a very curious manner. There is a con- 
siderable thickness of soft material, consisting partly of loose 
calcareous sands and partly of comminuted shells, with occa- 
sionally a layer of decomposed but not broken shells. In 
this mass are great blocks of irregular shape, lying often 
in the direction of some falsebedding rather than horizontally. 
These are indurated by so great an amount of calcareous 
matter, that where the sand was originally prevailing they 
are hard and gritty; where the shell fragments were once 
the main constituent they become excellent building stone ; but 
from their irregularity, working them must be somewhat pre- 
carious. In this quarry a geologist cannot fail to be struck 
with the singular complexity of the succeeding deposits, which, 
as will be seen, must represent in time the period when the 
far-famed stone of the Isle of Portland might have been 
forming. One can see represented as in a picture many of 
the features of that ancient land, on which but little further 
to the south flourished the cycads and conifers of the Purbeck. 
Here one may almost see the petrifying spring issuing from 
the underlying limestones, by its consolidated deposits of calc- 
tuif ; there one may trace the winding course of the ancient 
river, with its stone-covered base and muddy banks, its channel 
now filled with carbonaceous clay. Here is represented the 
tranquil lake, in which the calcareous matter sank to rest or 
was precipitated ; and there, perhaps, the remnant of the soil 
which once covered the dry land, but was redistributed on its 
submergence. The teachings of this quarry are most in- 
structive and interesting, though one unversed in field geology 
might need some guide, philosopher, or friend, to read them 
for him aright. 
Out of the Isle of Portland itself, the best stone is that 
obtained from the Yale of Wardour, through which the South 
Western Railway runs between Salisbury and Templecombe. 
There are many large quarries about Tisbury which send stone 
away far out of the district, though less appears to be worked 
there now than there formerly was. This stone is on the same 
geological horizon as that which is found in the great quarry 
at Swindon, and with one exception all the quarries are 
excavated for this. It is, however, of a very superior quality. 
It is scarcely a limestone, but rather a calcareous freestone, for 
it is composed of very fine grains of sand consolidated by 
calcareous matter. It is sometimes obscurely false-bedded, and 
