Haworth. | Physical Properties of the Tertiary. 267 
consequently the only essential feature to produce the mortar beds 
structure is to have a sufficient amount of the cementing material 
to hold any mass of sand or gravel, or a mixture of the two, together 
with relative firmness. In fact it frequently happens that the clay 
earried but litle sand and no gravel whatever, but is cemented 
together in a more or less firm mass so that it too has been generally 
designated by the term mortar beds. These records show that the 
cementing material is exceedingly irregular in its distribution. Gen- 
erally it is most abundant some distance above the underground 
water, frequently near the top of the well. In no instances known to 
the writer is the cement found in the same horizon with the ground 
water. In a few instances only, such as Grant county well No. 3, 
is there any of the cementing material below the water. If we use 
the presence of the calcareous cement as a criterion for judging 
the mortar beds, from the well records the same as from surface 
exposures, we must conclude that they are in general as near the 
surface as they are its base. 
In studying the physical properties of the Tertiary it is necessary 
to emphasize the conditions already stated, that the so-called mortar 
beds are simply the sand and gravel and clay materials cemented 
usually with caleareous cement. ‘The real stratigraphic conditions 
probably do not depend upon the presence or absence of cementing 
material, but rather upon the continuity of beds of like material. 
A stratum of gravel which is not cemented should be considered as 
important as though it had chanced to have its individual constitu- 
ents held tegether by a cementing material of some kind. Yet in our 
study of the subject we are usually inclined to regard the beds 
Which are cemented inte a firm rock as more important than softer 
materials. It is necessary, therefore, to look with considerable care 
at the character of the cementing material, and to determine if pos- 
sible its origin and the manner of its formation. 
THE CEMENT. 
The cementing material of nearly all the Tertiary sands and 
eravels which appear in the form of sandstones or conglomerates 
is calcium carbonate. A few exceptions are known to this rule. 
There is a sandstone near Long Island, in Phillips county, which is 
