412 
THOMPSON YATES LABORATORIES REPORT 
The appearance of the deposit coating the Vyrnwy Oswestry Aqueduct is more 
characteristic, a uniform fine coffee ground material, almost black in colour, coats the 
iron pipes uniformly all round, varying from -L-inch to |--inch. In the case of the 
brick culverts only the portion of the brickwork covered by the water is coated. In 
the iron pipes there are innumerable limpet shaped incrustations of various sizes from 
a split pea to two or more inches in diameter, they are ^--inch to one inch in height. 
They are covered by the deposit, when cut into they are composed of alternate layers 
of red and black rust-like material. The odour of the deposit is characteristic, it is 
more metallic and aromatic than that ot freshly turned earth. 
After drying and incinerating a very abundant ash is left. Iron is present in 
large quantities, and the yellow brown colour is, no doubt, due, in this instance as in 
other cases, to the presence of this metal. Manganese is also present, and the dark 
black colour is probably due to it. 
Microscopic Appearances 
Wherever the deposit occurs in the unfiltered water, whether in Lake Vyrnwy, 
or along the aqueduct, or at Oswestry, the appearances under the microscope are 
essentially the same. The bulk of the deposit consists of irregular flakes of a soft 
material of a characteristic golden brown colour, numerous silicious particles, a considerable 
amount ot vegetable debris, but remarkably few green algae of any kind. The 
absence of green algae is very noteworthy, it is quite unlike what occurs in river 
water, and is no doubt related to the composition of the water. The higher green 
forms of aquatic plants are also conspicuous by their absence from the lake. The 
number of bacteria present are comparatively small, and this is corroborated by the 
culture experiments which have been made by me upon an extended scale. The 
golden brown irregular masses have imbedded in them or sticking to them all kinds 
of debris. They are soft, because they can be flattened out under the coverslip, and 
they appear to be composed of some gelatinous material impregnated with the yellow 
oxide of iron. They often show no trace of structure, but flakes will be met with, 
which, on very careful examination with the high power, show passing through them 
one or more distinct hyphae. I have been able to observe these hyphae in the other- 
wise structureless superficial layers of the limpet-like incrustations of the iron pipe 
previously alluded to. 
Fig. I (Plate II) shows very well, magnified one thousand diameters, an 
irregular golden brown mass. In this photograph it appears very difficult to relate the 
gelatinous mass to the hypha shown running through it, but in Photographs 2 and 3 
of younger fragments equally magnified one thousand diameters, the gelatinous 
material assumes much more the character of a sheath to the hypha. When the 
material which clings to the copper gauze screen, previously referred to, is examined, 
or when the deposit obtained by centrifugalizing the water of the lake is exanrned, 
