Cornwall and South Devon. 345 



identical with such as are seen in the subjacent carbonaceous 

 rocks: these limestones to the eastward gradually thin out to 

 nothing, by irregular seams and fiat insulated cakes, among 

 true killas slates, but their earliest introduction is manifestly 

 by thin calcareous courses containing the characteristic Pether- 

 win fossils, among the underlying carbonaceous rocks, as may 

 be seen south of Landue mill near Launceston : these lime- 

 stones and associated slates are at times as abundantly loaded 

 with the remains of ancient life as any of the secondary rocks. 

 I have seen, in short, masses of lime-rockwhich decomposition 

 showed to be concretionary aggregates of organic structure : 

 of these I have been fortunate enough to obtain a very large 

 and varied assortment, many of them as yet undescribed: 

 among other large specimens of the beautiful Clymenia, I have 

 one which is nine inches in diameter. 



This lowest member of the killas group does not appear at 

 all on either the east or the south of Dartmoor, and is first 

 met with on the south-west of it, a little north of Borringdon 

 wood, from which its southern line is of course the north one 

 of No. 2, already described, as far as a little south of St. Ives, 

 from whence it mantles round the inner zone of carbonaceous 

 rocks (which closely invest the Bodmin Moor granite on the 

 north and north-west as far as near Michaelstow, on the south- 

 south-west of Camelford), beyond which, falling in again with 

 No. 2, it accompanies it to the sea on the south of Port Isaac, 

 as before adverted to s , and does not appear afterwards in any 

 of the southern sections, a circumstance which, coupled with 

 the interposition of No. 2 along the Padstow estuary and to 

 the eastward of it, proves that the fossiliferous beds of Pether- 

 win are not conveyed to St. Columb-Porth, Newquay, &c, 

 as has commonly been supposed. 



The accumulated evidences of its superposition, with regard 

 to the plant or carbonaceous rocks, are so strong, that any 

 attentive observer must admit that this series overlies and 

 passes downwards into them, by far more abundant and con- 

 clusive instances of simple section, gradation and alternation, 

 than even those carbonaceous rocks present on the north of 

 Devon, where they are now admitted on all hands to pass 

 by insensible transition into the older group of Exmoor : 

 the evidences of the former are certainly far more abun- 

 dant and demonstrable than anything of the kind I have ever 

 met with elsewhere, but exhibited at times on so vast a scale, 

 that the fidelity of their details is apt to be overlooked in the 

 magnitude of their proportions : in one instance, for example, 

 on the west bank of the Tamar, a traverse of six miles of 

 country, viz. from about two miles east of Petherwin to South 



