CLAYS OF BOYEY TEACEY, DEVONSHIEE. 
1027 
Eliminating these beds, we have no sand in the series below the uppermost bed of 
lignite (No. 5) excepting No. 27, which occurs in all the sections, and, indeed, consti- 
tutes a marked feature in the deposit as exposed at the “ Coal-pit.” It is 133 inches 
thick in the first section, no more than 19 in the second, and dwindles to 10 inches only 
in the third; but no bed is more continuous or better marked: its comparatively 
bright colour catches the eye, and indicates its presence along the entire length of the 
excavation. It attains a still greater thickness in the western wall of the pit. Between 
the first and thhd sections it forms an inclined plane 680 feet long and 123 inches high ; 
or base : height = 8160 : 123=rad : tan 52' ; so that, great as the attenuation is, it merely 
produces a gradient of 1 in about 66, or an inclination of less than one degree. 
The sections show that a similar eastward dimmution of thickness characterizes the 
28th bed. 
This attenuation, like the thinning out of the beds previously mentioned, (which, it 
may not be out of place to remark, is in the direction of the Strike of the deposit,) is 
probably an indication, were one needed, that the detrital layers were formed at the 
expense of the Dartmoor granite. 
The sections agree in naturally dhiding themselves into three parts or series, viz. — 
1st. The bed No. 1, of S^\js'DY Clay, containing angular and subangular stones. 
No stones of any kind were met with below this. 
2nd. The beds from the 2nd to the 27th, both inclusive, composed of sand, clay, and 
lignite. 
3rd. All the beds below the 27th, consisting of clay and lignite only*. 
It appears that that portion of the age of the deposit, which is represented by the 
first (that is, lowest) forty-five beds was unmarked by the deposition of sand within that 
area. Forty-four beds of lignite and clay, ha\ing an aggregate thickness of upwards of 
47 feet, succeed each other alternately in regular unbroken order ; the next bed, how- 
ever (28th in the sections), instead of being a mass of vegetable matter, as was due, is a 
second bed of clay, and, in the first section, of unequalled thickness ; this is followed by 
a thick bed of sand, the first which presented itself. Clearly some change must have 
occurred. Had the accumulated deposit so far shallowed the waters of the ancient 
lake \ Had it conveyed its western margin so far eastward, that sand was to be hence- 
forward deposited in the area hitherto appropriated to clay, instead of further west as 
heretofore \ If so, it might have been expected that the change would have been less 
sudden. No sand whatever had previously occurred. Moreover, on this hypothesis it 
is reasonable to suppose that sand would have been largely deposited in future, instead 
of which the old order (of clay and lignite alternately) is continued for eighteen addi- 
tional beds, increasing the depth of the deposit by nearly 40 feet ; indeed, omitting the 
two arenaceous beds (9th and 11th) which occur only in the first section, we have no 
more sand until the uppermost bed of lignite in the sections had been formed. In no 
instance does the lignite rest on or support sand, but always clay. 
* See Plate LIII. 
7 A 
MDCCCLXII. 
