STATE GEOLOGIST. 97 
Per Cent. 
STUDY RAS: Geet On A rae Fe > Ss ne PO rt oO 8.75 
NING DROW TONE ios & eee LON Cal ARORA tia hoes ele tee SRS staan ie 
LENSYETEN® roe as ii wana TEI WES CR vat aa Ane ARR si a rs uot gS a eRe 2.78 
Carbonaterolecal Chump reir aie ee ited 1 ave nee 79.21 
Carbonate of magnesium........... UP OSC tae ene ans 2.67 
93.41 
This analysis is characteristic, though the amount of clay mixed with 
the marl causes its proportion of silica and alumina to rise a little at the 
expense of the carbonate of lime from time to time. As clay must be 
added in any case, this is no disadvantage except possibly in keeping 
uniform mixtures. The known extent of this field is not great and is 
under control of the two companies now established. 
Another marl area is in northeastern Sandusky county and north- 
western Erie county. The Sandusky Portland Cement Co., located at 
Bay Bridge, has nearly exhausted its bed of marl which was not of large 
proportions originally. It has supplied material for a considerable indus- 
try for more than a decade. The Castalia Portland Cement Co., at Cas- 
talia, three or four miles south of Bay Bridge, has a much larger bed and | 
a larger plant. 
Travertine.— Associated with the marl beds in the Castalia district 
is a layer of Travertine, or calcareous tufa, deposited probably from 
former overflows of the great Castalia spring, which wells forth in 
volume sufficient to make a small stream. ‘This underground river, for 
it is nothing else, maintains at present a considerable lake or pond, and 
in times past probably made a much larger area of swamp land. Over 
this area, the travertine has been deposited, in some places as much as 
three or four feet thick, though generally much less. It is substantially 
pure carbonate of lime, showing a content of 99.4 per cent calcium car- 
bonate. | 
It is deposited as carbonate, from the breaking down of calcium bi- 
carbonate as it emerges from the underground water-course, and is ex- 
posed to the air, heat and motion of the stream. Though travertine can 
hardly be called a regular source of Portland cement material, it is used 
at the Castalia works with very excellent results. 3 
i—S. G- Bull. 3: 
