1852.] WESTON ON PORTLAND. 119 



inclined plane, but, after passing "Weston (see fig. 11), the surface 

 rather sinks down by terraces to the Bill, so that streams are con- 

 stantly flowing to the South from the bassett-edges of the Lower Pur- 

 Fig. 1 1 . — Longitudinal Section of the Isle of Portland. 



N. S. 



Weston. Southwell. Shingle on 



4 V- Purbeck. 



1. Kimmeridge Clay. 2. Portland Sand. 3. Portland Oolite. 4. Purbeck beds. 



beck strata. These features have doubtlessly resulted from partial 

 denudation. The superficial covering of beach-pebbles proves a 

 co-existing and co-extensive sea, and their rolled character equally 

 points out the long period during which the sea must have acted on 

 the Southern part of the island. But the local extent of the beach 

 seems also to show that the Northern portion of the island was stand- 

 ing fully emerged from the ocean, while the Southern was still under 

 its influence. May we not, therefore, infer from these premises that 

 the Island of Portland has experienced an elevatory movement sub- 

 sequent to that which it felt in common with the whole Weymouth 

 district ? For, as by the protrusion of the great boss of Forest Marble 

 the Northern extremity of the island was tilted up, leaving the Southern 

 portion a littoral region, so there must have been a second upheave- 

 ment, by which the Southern part was elevated and enabled to carry 

 up to its present height on the shoulders of the Purbeck the beach- 

 pebbles of the bed No. 7, fig. 10. 



We have seen that the Purbeck formation does not stop at the " 

 centre of the island, as hitherto considered, but exists also at its most 

 Southern extremity ; and I believe, from the specimen of fossilized 

 wood which I saw near the Government Railway on the N.E. side of 

 the island, and which I was told, on good authority, came from a 

 neighbouring quarry, and from the nature of the ground over which 

 I walked on my way to the Bill, that the Purbeck will ultimately be 

 found to be co-extensive with the entire subjacent Portland oolite. 



In conclusion, I would observe that the Isle of Portland aifords 

 an instructive view of the rise of rivers, and may enable us to specu- 

 late upon the real geological locality of the river Wey at Upway. 



In Portland we have confessedly a mass of land completely isolated, 

 and yet, on proceeding Southward beyond Weston, we find, as already 

 noticed, copious springs. It will be evident by a reference to a sec- 

 tion of that island (see fig. 11), that these springs could not possibly 

 have a source beyond the North escarpment, both from the structure 

 and the stratification of Portland ; and yet we see that this limited 

 region, with the acknowledged laws of the atmosphere and caloric in 

 relation to capacity for absorption of moisture, aifords an ample appa- 

 ratus for the production of perennial streams by unceasing conden- 

 sation of aqueous moisture. 



Now the River Wey wells up from the Portland Oolite at the North 



