ERRATIC BLOCKS OF THE BRITISH ISLES. 133 
(11x9x6 inches); (b) Well-polished and striated block (9x8 x 2} 
inches) ; (c) well-striated block (7422 inches); (d) Block of ‘ encrin- 
ital limestone ’ (8x 5x3 inches) partly marmorised. 
la. Millstone-grit various and numerous towards the southern 
end of the ‘ till,’ two miles south of Harlow, where it ends off abruptly 
upon the London clay in situ. . 
2. Permian.—Fragment of ‘ Réthschiefer ’ and marl-slate. 
3. Bunter.—Quartzite and quartz pebbles (the largest 7 inches). 
4. Keuper.—Calcareous basement breccia. 
5. Rhetic.—Traces of ‘ bone-bed ’ on slab of limestone. 
6. Lias.—(a) Concretionary ironstone from the M. Lias (one block 
7x 5x14 inches); (b) Block of hard shelly limestone containing 4 vicula 
inequivalvis, Ditrypa quinquecristata, and plates of Osirea liassica (?); 
(c) Gryphea incurva (rather common); (d) Pholodomya ambigua (iso- 
lated and worn; (e) Modiola % gibbosa as in the Lias of Kilsby 
(Northants); (f) Ammonites (Aigoceras) angulatus (?) dispersed on a 
slab of grey limestone. 
7. Great Oolite.—Slabs of unfossiliferous limestone, very similar to 
beds exposed at Great Ponton. 
8. Cornbrash.—Rounded block of tough shelly limestone (10x63 
inches); angular block of more shelly limestone with Plewromya, sp., 
and Nucula Waltoni. 
9. Oxford Clay.—Calcareous nodules; shale containing small am- 
monites of the Jason group (as at Fletton, near Peterborough); Amm. 
varicostatus; Amm. vertebralis (fragment); Belemnites Oweni (puzost- 
anus) rather common; Gryphea dilatata; Gryphea bilobata. 
9a. Calcareous Grit.—Rolled fragment of cast of Ammonites solaris 
(plicatilis) ? ; 
10. Kimmeridge Clay and Portland Sand.—Ostrea deltoidea; 
Ostrea expansa; Ammonites biplex; several fragments (one apparently 
complete in a large concretion) (12 x 10 x 43 inches). 
One fragment of Jurassic (?) Ammonite, sp. (?) 
11. Purbeck.—Slab of argillaceous limestone with Cyprides ; block 
of sulphurous limestone with lignite (10x 6x3 inches), striated (no 
direct evidence of its geological age). 
12. Cretaceous.—Boulder of Red Chalk (Lincolnshire or Norfolk) 
(7x6x5 inches); boulders from the harder beds of the Upper Chalk; 
very common, often grooved and striated. 
13. Roughly cleaved Slate from Charnwood. 
Remarks.—(1) Rolled sarsens and septaria from the Eocene are not 
reckoned as ‘ erratics.’ (2) The summit of the hill pierced by the sewer- 
age-works is 252 feet, and here the boulder clay was pierced to 32 feet 
without reaching the bottom of the deposit. Two rolled fragments of 
crystalline rock have been found more recently, both bearing a 
resemblance to some Derbyshire dolerites. 
Nore.—In the identification of the specimens assistance has been 
freely rendered by members of the staffs at the British Museum 
(Natural History) and at Jermyn Street Museum, and is here gratefully 
acknowledged. The works of the late John Phillips, F.R.S., and 
Robert Etheridge, F.R.S., have been freely used. 
