"As the two walls which form the new covings... are not parallel... but inclined, presenting an oblique surface towards the front of the Chimney, and as they are built perfectly upright, and quite flat, from the hearth to the top of the throat, where they end... an horizontal section of the throat will not be an oblong square; but its deviation from that form is a matter of no consequence; and no attempts should ever be made, by twisting the covings above, where they approach the breast of the Chimney, to bring it to that form."