CHAPTER XVIII.. Obstruction of Drains.

OBSTRUCTION OF DRAINS.

Tiles will fill up, unless well laid.--Obstruction by Sand or Silt.--Obstructions at the Outlet from Frogs, Moles, Action of Frost, and Cattle.--Obstruction by Roots.--Willow, Ash, &c., Trees capricious.--Roots enter Perennial Streams.--Obstruction by Mangold Wurtzel.--Obstruction by Per-Oxide of Iron.--How Prevented.--Obstructions by the Joints Filling.--No Danger with Two-Inch Pipes.--Water through the Pores.--Collars.--How to Detect Obstructions.