Geology of the South-east of Devonshire. 



437 



Ven€rupis Irus, Lamk. 



Corbula nucleus, Lamk. {Syn. C. rugosa, Bast.) 

 according to Lamk. M. 



striata, Lamk. B. 



Pandora rostrata, Lamk. M., It. 

 Thracia pubescens, Leach. M., Sic. 

 Mya arenaria, Linn. 

 Lutraria rugosa, Lamk. 

 Psammobia vespertina, Lamk. M. 



f Solen antiquatus, Linn. B. 



Solecurtus, De Blain. 



V 



coarctatus. Med. 



Solecurtus strigilatus, Linn. M., B., T., Sic. 

 Solen ensis, Linn., Penn, Sic. 



• legumen, Linn., Penn. Med., B., T. 



purpureus, Turton. 



siliqua, Linn., Penn. 



Panopaea Aldrovandi (Mya glycimeris), Men. de 



la Gr. M. 

 Gastrochaena hians, Brocchi. (Mya dubia, Penn.) 



M., B., It. 

 modiolina. Lam. It., Sic. 



2. Period prior to the most recent changes of relative level of land and water, 



and of climate. 



§ 1. Surface-soil. — Throughout South Devon the surface-mould partakes of the 

 nature of the subjacent rock. The map (PL XLI.) illustrating this memoir will 

 sufficiently show how many formations, composed of very different constituents, 

 are closely associated within its limited area, so that perhaps no other district affords 

 better opportunities for observing the influence of soil on natural vegetation, or 

 indicates more clearly the requirements of particular plants. Geology in its appli- 

 cation suggests various considerations, which the labourer in the pure science has 

 too much neglected ; and very many more consequences flow from the original ar- 

 rangement of the mineral masses of a district than at first appear. 



On the slopes of the hills of the slate district of South Devon, and immediately 

 beneath the superficial soil, the edges of the laminse of the slate are disturbed in a 

 very remarkable manner, and frequently to the depth of several feet. In general, 

 they present a simple curve, but occasionally they are most curiously contorted as 

 in fig. ], which represents a portion of a section at Goodrington, Fig- 1- 



near Ashburton. In every case the curve is directed outwards. 

 By the action of frost on the exposed edges of inclined slate rocks 

 the lamiuce separate, earthy matter is carried in between them, and 

 thus the space they required is gradually increased. I have no 

 doubt that in a similar process we have the true explanation of the 

 appearance above described ; and though it would be hazardous to 

 say that it may not have resulted from long-continued action of the actual frosts, 

 yet when we consider the great extent to which this separation of the leaves of the 

 slate has been carried, and the very inconsiderable depth to which frost at present 

 penetrates in this part of England, we seem to require a period with a lower tem- 

 perature and the action of deeper searching cold. 



In some places, as in most valley sections, and above the raised marine beds of 

 the modern period, are thick accumulations of angular fragments, brought down 



VOL. VI. SECOND SERIES. 3 L 



