58 STEPHEN TABER 
transitional stages toward the Bertie waterlime. The gypsum is 
highly argillaceous and in places grades into gypsiferous shales. 
Partings of shale, ranging in thickness from a fraction of a centi- 
meter up to several meters, are usually present, dividing the gypsum 
into several beds. These beds thin out and disappear, so that their 
number and thickness vary greatly in different districts. In many 
sections they are entirely absent. Gypsum may be found in small 
quantities all the way from the bottom to the top of the Camillus 
shale, but usually most of it is near the top. 
The Onondaga limestone is commercially the most important 
of the limestone beds, and therefore there are many quarries located 
all along its outcrop; but the Cobleskill and Manlius limestones 
are also being quarried at several places. ‘The lower layers of the 
Onondaga limestone, locally known as ‘“‘gray limestone,” have a 
well-developed crystalline texture similar to that of marble. The 
limestone forming the upper portion is bluish gray in color, dense, 
fine-grained, and contains numerous nodular concretions of chert 
or hornstone. Microscopic examination shows that the “blue lime- 
stone’’ consists essentially of irregular grains of calcite and small 
crystals of pyrite, while rhombic crystals of calcite may occasionally 
be distinguished. 
The chert varies in color from light bluish gray to almost black, 
and on freshly fractured surfaces is often difficult to distinguish by 
color or texture from the inclosing limestone (see Fig. 6). It is 
irregularly distributed, occurring often in small isolated nodules, 
though more commonly the nodules are arranged in well-defined 
rows or layers, and in places these layers of disconnected nodules 
pass by gradation into more or less continuous and uniform layers 
or bedded veins, which may be 3 cm. or more in width and extend 
for distances of many meters. The chert masses have evidently 
been formed through replacement of the limestone, for some of 
them contain fossils in which the details of structure are perfectly 
preserved. On weathered surfaces the chert, because of greater 
resistance, stands out in sharp relief. Microscopically the chert 
is cryptocrystalline, and the boundary between limestone and 
chert is not sharply defined. In passing from limestone to chert 
there is a gradual though rapid decrease in calcite with a correspond- 
