BUILDING STONE. 635 
regular until they become polished by wear, and then they are dan- 
gerously smooth. For construction purposes the stone has proven very 
durable, and the best foundations can be secured at small expense if made 
from this stone. It is also used for macadamizing the streets, and 
recently it has been found that a foundation of the Sandusky blue lime- 
stone can be advantageously overlaid by a thin coat of the white limestone 
which binds and cements the road-bed. 
All of the quarries which in the tables are indicated as existing in 
the corporate limits of Sandusky are essentially one, as they produce 
the same material, and only ina single case has a quarry been sunk to the 
level of the underlying white limestone. About one hundred and eighty 
houses in the city have been constructed of this stone. The specimens 
sent to the National Museum from various quarries are identical in their 
minutest structures. They are bluish-gray in color, compact, and present 
a fine appearance, however dressed. Although they effervesce rapidly in 
acid, they are quite magnesian, and under the microscope they are seen 
_ to consist of fossil fragments, among which a multitude of little rhombo- 
hedral crystals are developed. In the center of each one of these 
rhombohedrons is a black spot, which, upon close examination, is found 
to consist of pyrites. Sometimes, instead of a single spot, there is a large 
number of dust-like particles, which give to the stone a very marked and 
characteristic appearance. These are so numerous that it can scarcely 
be doubted that they impart the characteristic color to the stone. That 
they are situated, however, in the exact center of compact crystalline 
material cannot but have an influence in protecting them from disinteg- 
ration, and there is no evidence that the presence of this ingredient has 
proved deleterious to the stone. 
The white underlying limestone is what is called a cutting stone, 
and can be raised in blocks as large as can be handled. It is more highly 
fossiliferous to the unaided eye than the blue limestone, but under a 
microscope it is less so, and there is a much larger number of the rhom- 
bohedral crystals which correspond to its more magnesian character. 
At Point Marblehead the limestone quarries are all located in a 
terrace lying a few rods from the beach, where the thickness of the forma- 
tion quarried is from 15 to 26 feet. Already 20 acres, as estimated, have 
been excavated to this depth. 
These quarries are among the most famous of northern Ohio, and 
their location directly on the shores of lake Erie, and the heavy stones 
