C 583 ] 
hundreds of yards ; but in all thefe, a very few only 
excepted, the whole of each is not one continued 
mils, but is again fubdivided into a great number 
of thin laminae, that feldom are more than one, two, 
or three feet thick, and frequently not fo much. 
39. Befide the horizontal divifion of the earth into 
ftrata, thefe ftrata are again divided and fhattered by 
many perpendicular fiffures, which are in fome places 
few and narrow, but oftentimes many, and of con- 
fiderable width. There are alfo many inftances, 
where a particular ftratum (hall have almoft no 
fiffures at all, though the ftrata both above and be- 
low it are confiderably broken: this happens fre- 
quently in clay, probably on account of the foftnefs 
of it, which may have made it yield to the preffure 
of the fuperincumbent matter, and fill up thofe fif- 
fures which it originally had ; for we fometimes meet 
with inftances in mines, where the correfpondent 
fiffures in an upper and lower ftratum are interrupted 
in an intermediate ftratum compofed of clay, or fome 
luch foft matter. 
40. Though thefe fiffures do fometimes correfpond 
to one another in the upper and lower ftrata, yet this 
is not generally the cafe, at leaft not to any great di- 
ftance: thofe clefts, however, in which the larger 
veins of the ores of metals are found, are an excep- 
tion to this obfervation ; for they fometimes pafs 
through many ftrata, and thofe of different kinds, to 
unknown depths. 
41. From this conftitution of the earth, viz. the 
want of correfpondence in the fiffures of the upper 
and lower ftrata, as well as on account of thofe ftrata 
which are little or not at all fhattered, it will come to 
pafs. 
4 
