PENCE—THE PONT-Y-PRYDD   ARCH.                           19

first class and 4 % second class material of all the bricks moulded;
the remaining 1 % is lost in the various stages of the work.

In some parts of the immense pampas firewood is exceedingly
scarce, and tall thistles and other large weeds are the only fuel avail¬
able. In such cases short straw or other organic substance is often
mixed in the clay when prepared for moulding. The bricks are then
easily burned, some 18 hours fire being sufficient, but the material
obtained is very porous, of little strength, and otherwise defective.

Perhaps it should be mentioned that in the aforesaid countries
stone is not employed in the construction of bridges and culverts,
except when found in the vicinity of the structure erected, and there¬
fore the demand for bricks is correspondingly increased.
 

THE PONT-Y-PRYDD ARCH.
 

By W. D. Pence, Assistant in Applied Mechanics.

There are often associated with engineering structures of lesser
magnitude many facts which, when known, prove to be of real in¬
terest and value. A notable instance of such is the Pont-y-Prydd
masonry arch at Newbridge in south Wales. In presenting the fol¬
lowing brief sketch, in which are collected from various sources the
leading facts in regard to this arch, it is hoped to secure to its de¬
signer and builder some portion of the credit due him for this, his
masterpiece.

In 1746 William Edwards contracted to bridge the river Taff
at the site of the present Pont-y-Prydd, and completed a three-span
^arch, which, on account of its admirable execution, gained for its
builder much praise. However, it seems that Edwards had failed
to provide sufficient water way for the passage of extraordinary
freshets, for one of the latter occurred only two and a half years after
the completion of the bridge. The mountainous character of the up¬
per Taff watershed and the union of several important branches
above Newbridge caused a rapid concentration of water at the latter
point during times of flood. In the particular freshet above referred
to, much drift in the shape of trees, haystacks, etc., lodged against
the   piers   of the newly   completed structure   and the   waterway