*S8 Sir R. I. Murchison on the Discovery 



arc younger than those of Poravor and Gorran Haven. Time and 

 careful researches must, however, determine this question of detail, 

 and all I can now express is my opinion, that the quartzose rocks 

 and killas which extend from the tracts above alluded to, to the 

 mouth and centre of the bay and harbour of Falmouth (probably 

 much farther to the SW.), are of Silurian age also. 



The energy of Mr Peach having thus afforded us the key by which 

 new lights are thrown on the succession of Cornish strata, I cannot 

 but hope, that when the Government geological surveyors revisit 

 Cornwall, they will define the exact demarcations between these Si- 

 lurian masses and their overlying Devonian neighbours. In fact, I 

 have, within these few days, been talking over this subject with my 

 friend the Director-General of the survey, and he has pointed out to 

 me, on his detailed map, how, from the enormous flexures which the 

 strata have undergone in their range from Devon into Cornwall, 

 it is highly probable that Silurian rocks (the equivalents of those 

 alluded to) may be recognised in other parts of Cornwall. Thus, the 

 quartzose rocks of Pydar Down or Moor, to the north of St Columb, 

 which form an E. and W. axis, dipping to the N. and S. under fos- 

 siliferous Devonian strata, may (he thinks) prove to be also of Silu- 

 rian age. But, forbearing to speculate on the probable results of 

 future researches, it is my decided belief, that the slaty rocks, con- 

 stituting the great southern headland of Devonshire ; at least all the 

 schists, &c., to the north of the Start Point, will eventually be classed 



■ with the Silurian group of South Cornwall : for if the Plymouth 

 ■group of limestones, so prolific in animal remains, afforded us the 



means of deciphering the age of less clearly developed zones on the 



■ same horizon in Cornwall, the Silurian types collected by Mr Peach 

 may enable us to carry out a more correct classification in still older 

 strata, from Cornwall into the obscure southernmost promontory of 

 Devonshire. In the mean time, confining ourselves to what we now 

 know, it is manifest that Cornwall exhibits in ascending order, — \st^ 

 a band of true Silurian rocks ; 2(i, a zone of intermediate character, 

 forming a transition between the Silurian and Devonian systems ; 

 3o?, a copious Devonian system, characterized by lower and upper 

 limestones; and, 4fA, a limb of the culmiferous or carboniferous 

 basin. 



This view will, I trust, be perfectly intelligible to the members of 

 your Society who have occupied themselves with the consideration of 

 this branch of geology, and on which Mr R. Q. Couch has recently 

 written with perspicuity and talent. I doubt, however, if anything 

 I have stated will make an impression upon one of that number, my 

 good-humoured antagonist the Rev. D. Williams, whose views of the 

 Cornish succession of strata seem to be opposed to those of all his 

 contemporaries. Geologists, however, who have long lived in Corn- 

 wall, and have so well illustrated its mineral styucture, will, I am 



