LOWER LIAS : LYME REGIS. OO 
subdivisions differ to the extent of from 5 to 15 feet in various 
places. This may be due to original variations in the thickness 
of the strata, but it may also to some extent be attributed to 
a difference in pressure, the strata in some places being over- 
laid by thick and heavy accumulations, while in others they are 
at or near the surface. 
The earliest geological descriptions of this coast-line were by 
De la Beche, who noted the leading lithological divisions in the 
strata and their organic remains, and gave an excellent 
pictorial diagram of the cliff-sections.* 
Many years afterwards the Lower Lias beds were examined 
and described in detail by Dr. Wright, and subsequently the 
subdivisions of the Middle and Upper Lias were investigated 
very carefully by Mr. E. C. H. Day, who was assisted largely 
by Mr. R. Etheiidge. These observers have furnished the 
greater part of our knowledge concerning the distribution of the 
organic remains, but to Dr. Wright especially \ve owe the 
adoption of that system of grouping the beds into Zones, 
which had been go ably marked out by Oppel. The help of 
local workers is however of the utmost importance to those 
who can spend but a few weeks in a district, and much of 
our knowledge of the horizons of fossils is due to the labours 
of the fossil- collectors, and especially to Samuel Clark and 
Robert Hunter of Charmouth. 
De la Beche, in his account of the Lias, adopted the nomen- 
clature ov William Smith and Conybeare, so that his main 
divisions do not correspond with those now adopted, us will be 
eeen from the accompanying table : 
MODKBX GROUPING. 
FT. 
Upper Lias 70 
Upper Lias Marls * - - Middle Lias 345 
\- Lower Lias 485 
T . , . f Blue Lias 
Lias Limestones - '{ White Lias - 
f Black Shales - - \- Rhaetic Beds. 
Lower Lias Marls - ( (Jrey Marlg . . / 
The full thickness of the Lias is thus about 900 feet, and it is 
desirable to describe the beds as far as possible in detail, as 
nowhere else in our area have we such a connected series of 
exposures.t 
* Trans. Geo). Soc., ser. 2, vol. i. pp. 40-47, and Plate VIII. ; vol. ii. pp. 21-30, 
and Hate III. ; and Report on the Geology of Cornwall, Devon, and West Somerset 
(Geol. Survey), 1839, pp. 222-235. 
f My first acquaintance with the sections was made in 1873-74, when engaged, in 
conjunction with Mr. Clement Reid, in re-surveying portions cf the district. In 
1884 I examined the coast-section in detail, and constructed a horizontal section to 
show the relations of tlie several subdivisions. This was published Jn a condensed 
fcrni in 1886. See Report on Coast-erosion, Rep. Brit. Assoc. for 1885, p. 424; 
Geology of England and Wales, Edit. 2, 1887, p. 252 ; and account of excursion 
to Lyme Regis., Proc. Geol. Assoc., vol. xi. p. xxvi. (Reprinted). 
