294 
THE MIDDLE LIAS OF NORTHAMPTONSHIRE. 
the lamination was horizontal. Now when the hard compact 
stone has been quarried it is seldom possible to tell in what 
direction slialing will take place under ordinary weathering 
influences ; hence it is exceedingly probable that much of the 
stone would be dressed and placed in a very unfavourable 
position for its lasting qualities. The weathered portions have 
already developed those characteristics by which its proper 
position in a building may be decided. (3.) The hard stone 
lias retained its bluish-green colour owing to the fact that it 
has not been subjected to the action of percolating water 
and the gases contained therein ; hence, if it were used in 
a building, the ordinary atmospheric influences would pro¬ 
duce chemical changes in it such as have already occurred 
in the more porous or more superficial parts of the same 
bed, and these could scarcely be otherwise than detrimental, 
because they would be taking place first and most rapidly 
in the exposed parts. With building stones generally it is 
desirable that all chemical changes likely to take place 
through the presence of iron or other bodies should be com¬ 
pleted before their use—that is to say, for building purposes 
the seasoned stone is preferable to the green. 
Owing to the porosity of these weathered portions of 
the stone, which are chiefly used for building, a thicker 
wall is required than when bricks are used. 
I may remark that buildings constructed of marlstone 
can scarcely be distinguished at a little distance away from 
those built of the more ferruginous portions of the North¬ 
ampton sand. 
Bricks are sometimes made from the clays of the 
“ Spinatus” Zone, as at Market Harborougli; and I believe 
some of the lower beds of the “ Margciritatus ” Zone are 
so used at and near Banbury, though I have never seen 
bricks made from them in Northamptonshire. 
Road-Metal. —In those positions where the Rock-bed has 
been quarried most—that is, really where it is nearest the 
surface of the ground, the upper portion is generally rubbly 
in character, very much broken up, and the pieces too small 
for building purposes; this is used for road-metal still, but 
not very extensively, for slag from furnaces and Hartsliill 
stone find their way almost everywhere now, the former of 
these two being very inexpensive, and the latter much 
superior for public roads where there is considerable traffic. 
Of course, the harder portions of the Rock-bed have also been 
used for road mending. 
It might be thought that since the Marlstone Rock-bed 
has been so largely used for several purposes, quarries would 
