381 
occurred a great upheaval of Paleozoic rocks from the May- 
Hill district to the Mendips; and looking at the fact that the 
Yellow Sands in the neighbourhood of Sodbury—where this 
upheaval meets the Jurassic strata—are much thinner and of 
a slightly later date than the Cotteswold Sands proper—indi- 
cating the proximity of some barrier—I am inclined to put the 
date of this upheaval after the deposition of Lower Lias and 
just before that of Cotteswold Sands. 
The barrier raised by this upheaval—of which we may still 
trace remains in the belt of Paleozoic rocks which almost 
absolutely connects the May Hill district and the Mendips, by 
way of Tortworth, and the South Gloucestershire Coal Field— 
would have cut off the Dundry area most effectually from the 
Cotteswolds. Supposing that this upheaval took place after the 
deposition of the Lower Lias only, that gives us an amount of 
some 300 or 500 feet of strata above the Rheetics. 
If we glance down the line of country where the upheaval 
took place, we see that the newest strata in this line, of which 
they form a very small part, are Rhetics, and that therefore 
the height of the barrier would have been nowhere less than 
some 300 feet; but, possibly, towards Sharpness, where the 
Silurian is shewn, it would have been very much greater. We 
may therefore imagine an isthmus connecting the former 
Mendip island with the mainland, 7.e. Wales, etc., by way of 
Sodbury and Tortworth. 
Coincident, possibly, with the upheaval of what I will call 
the Tortworth barrier, I imagine another upheaval producing a 
prolongation of the Mendip axis towards the east. The fact 
that in the borings round London and in the east of England, 
New (Old?) Red Sandstone was met with at Richmond and 
Kentish Town—Carboniferous at Harwich—Old Red Sandstone 
and Devonian at Meux’s Brewery, London, and at Cheshunt— 
and Silurian at Ware—in no case overlain by Lias or Inferior 
Oolite, but generally by cretaceous rocks,* shews where the 
eastern shore lay in early Jurassic times. There is every reason 
* H. B. Woodward, Geology of England and Wales, 2nd Edition, 
Appendix, I., 1888 
