‘Parr IIL Szcr. ii.§ 2] JURASSIC. 785 
passed into universal use, and though some of them are uncouth English 
provincial names, they are as familiar to the geologists of other countries 
as to those of England. 
The Jurassic formations stretch across England in a varying band 
from the mouth of the Tees to the coast of Dorsetshire. They consist of 

Fic. 382.—MARSUPIALS FROM THE PURBECK BEDs. 
a, Jaw of Plagiaulax minor (Falconer) (?); b, same (nat. size); c, molar (8); 
d, Triacanthodon serrula (Owen) (nat. size). 
_ harder sandstones and limestones interstratified with softer clays. and 
shales. Hence they give rise to a characteristic type of scenery,—the 
more durable beds standing out as long ridges, sometimes even with low 
cliffs, while the clays underlie the level spaces between. Arranged in 
descending order, the following subdivisions of the English Jurassic sys- 
tem are recognized : | 

Maximum 
thicknesses. 
Feet. 
Zee et Upper fresh-water beds... 
~ &@ | Purbeckian...{Middle marine beds...... Rene Mewar crane sib suena 360 
235 Lower fresh-water beds... 
25 9 ; Orland StOMG acs cars9:n,o\o. ws eyateiale lols t avehet eel clea ae os 70 
AO | Portlandian . {Portland Sande ce re aan eee 150 
Kimmeridgian Kimmeridge Clay .................... aac 600 
cg @ | Corallian..... Coral Rag and Caleareous Grit ............00. 250 
— 0+ , 
coher 
ZO & | Oxfordian.... Oxford Clay and Kellaways Rock ............. 600 
8 ( (CO CENDTASM cc aici nielere sais © se ees sre a8 6 <b elgale 40 
3 | | Bradford Clay and Forest Marble (in Dorsetshire 
ro) rte aie OOUte ci LOU EUS)! o/s 620s 15.4.0, cin vies siciareie se pos oie/e d.e'eleke = 30 
a |Great or Bath Oolite with Stonesfield Slate (part 130 
= \aof Northampton:Sand)e sac. Wich aaaieads Oak's 
Bee iollcrs Wanth. Muller's Marth... sc. sets. esonosve de sine s 150 
cS) Cheltenliams beds \.. 4.) o/s ctw pena aiks grexoey wine 270 
Ks | Inferior Oolite.; Lower part of Northampton Sands, “ Dogger” 160 
E { of Vorkshire SiGe}. Fis P55 0c cre ode ae 
Upper Lias (Midford Sands).................. J Boome res Eine 400 
Ss NAIR ASLOMO MMI aiaters cats c winters «6 o's wrecele crate sie afi cte’e ae a ais.aiwes oan 200 
eI WonuOreladeiseir. wicreivicrs she eis bias oe CENT. SOLAN a ha Sale 900 
Although these names appear in tabular order as expressive of what 
is the predominant or normal succession of the beds, considerable difler- 
ences occur when the rocks are traced across the country. ‘Thus the 
Forest Marble attains a thickness of 450 feet in Dorsetshire, but dwindles 
down to only 15 feet at Blenheim Park. The Inferior Oolite consists of 
marine limestones and shales in Gloucestershire, but chiefly of massive 
3 E 
