Page:Transactions of the Provincial Medical and Surgical Association, volume 2.djvu/197

 serious inconvenience in the formation of sewers. The water which it yields is good, but, on boiling, becomes milky in appearance, from the carbonate of lime held in solution. From this rock issues the spring at the Hotwells, so much resorted to by invalids in former times. Its temperature is 74° Fahrenheit, and its specific gravity 1.00077. Each pint contains

The water obtained from the millstone grit is, for the most part, extremely pure. It occasionally, however, puts on a different appearance, from being tinged with iron, which abounds in this rock. The grit is a compact siliceous stone, and contains large quantities of quartz crystals called Bristol Diamonds, which are six-sided pyramids, frequently deposited on needles of iron, or manganese, or sulphate of strontia.

We shall not attempt any account of the other coal measures, as no part of the city is built upon them. They do not occur within a shorter distance than a mile and a half or two miles. For the same reason we shall pass over the next in order to these, or the dolomitic conglomerate, the first of the unconformable strata.