IN ILLUSTRATION

OF

VOLUME IV.

SECOND SERIES,

OF

THE TRANSACTIONS

OF

THE GEOLOGICAL SOCIETY

OF LONDON.

LONDON:

PRINTED BY RICHARD TAYLOR, RED LION COURT, FLEET Street. SOLD AT THE APARTMENTS OF THE GEOLOGICAL SOCIETY, SOMERSET HOUSE.

EXPLANATION OF

OF THE PLATES.

PLATES I., II. & III.

Illustrate Dr. Buckland and Mr. De la Beche's paper on the Geology of the neighbourhood of Weymouth and the adjacent parts of the coast of Dorset.

PLATE I.

Geological Map of the neighbourhood of Weymouth and the adjacent parts of the coast of Dorset.

The reader is requested to take notice that the authors do not profess to mark the exact limits of the lower Purbeck Beds in Portland, but merely to indicate their presence as the uppermost formation in the north end of that island.

PLATE II.

Series of Sections.-Colours the same as in the Map.

Fig. 1. Section from the Great fault near Upway to the Bill of Portland*.

Fig. 2. Section from the Great fault near Moigne's Down Farm to Ringstead Bay.

Fig. 3. Section from the Great fault near Poxwell to the signal station near Osmington Mills.

Fig. 4. Section from the Great fault near Sutton to the Sea at Ham Cliff.

Fig. 5. Section from the Great fault near Sutton to Jordon Hill in Weymouth Bay.

Fig. 6. Section from Abbotsbury Common over Linton Hill.

Fig. 7. Section from Abbotsbury Castle to Abbotsbury Swanery, showing the continuation of the Great fault.

Fig. 8. Coast section from Jordon Hill to near Boat Cove. The apparent curvature in the Oxford Clay and other strata at the east end of this section arises from an indentation of the coast: the strata have an E. and W. direction throughout, and dip rapidly N., and have not the bend here represented, by throwing the curves of the coast into a straight line.

Fig. 9. Coast section from near the termination of fig. 8 to Ringstead Bay. As the coast ranges along the line of direction of the strata, its indentations give these strata a false appearance of dipping in different directions: they form a small arch at Osmington Mills.

The Scale (in length) of fig. 1. is one inch to the mile; of fig. 2. to 10. inclusive, two inches to the mile: figs. 11. to 13. inclusive are on a larger scale, and fig. 14. two inches to the mile.

Fig. 10. Coast section near White Nore.

Fig. 11. Fault in the Cliffs, a little W. of White Nore.

Fig. 12. Theoretical diagram representing the manner in which different rocks may be seen in contact, in consequence of various degrees of denudation, on the same fault. Illustrations of this may be found in Sutton Valley ;-where there is little or no denudation, the Portland Stone and Chalk are in contact at the surface; where a denudation occurs to the depth of the curved line a a, the Portland Stone and Green Sand are in contact, on opposites sides of the fault; at the depth bb, the Portland Sand and green sand touch each other; and at the depth c c, the Kimmeridge clay touches green sand.

Fig. 13. Fault in the cliff west of Bridport Harbour.

Fig. 13 a. Eastern termination of the Bridport Harbour fault.

Fig. 14. Section from the cliff west of Bridport Harbour to Askerswell.

PLATE III.

Fig. 1. Tabular and proportional view of the strata in the Weymouth district.

a. Angular flints and plastic clay.

b. Chalk.

c. Chalk interspersed with grains of green earth (Craie chloritée).

d. Indurated green sand, with quartz grains and quartzose sandstone.

e. Greenish brown sands with indurated concretions.

f. Light brown sands. Fox mould.

g. Green sandy marl beds, with nodules similar to the cow-stone at Lyme Regis. h. Purbeck beds.

i. Dirt bed, above the Portland beds, frequently contains rolled calcareous pebbles, and fossil silicified trunks of large coniferous trees, and of Cycadeoideæ.

k. Best beds of the Portland Stone.

1. Compact light-coloured limestone, with beds, seams, and nodules of chert. m. Grey shelly beds, the base of the Portland Stone.

n. Green, brown, and grey sands and sandstones.

o. Brown and grey sandy marls, with indurated nodules.

p. Kimmeridge clay, contains an abundance of deltoid oysters.

q. Clay ironstone in the lower part of the Kimmeridge clay.

r. Upper grit beds, containing deltoid oysters: these beds are most fully developed near Sandfoot Castle.

s. Oolite differently developed in different places.

t. Brown sands, containing indurated nodules of calcareous sandstone.

u. Grey clay.

v. Larger deposit of calcareous grit, containing Gryphæa dilatata.

w. Oxford clay, grey marl, abounding in Gryphæa dilatata.

x. Rubbly and slaty Cornbrash limestones, alternating with clays and marls.

y. Slaty and shelly grey and brown limestones, containing Apiocrinites rotundus,

lignite, broken shells, &c.