2, PROF. T. G. BONNEY ON THE HORNBLENDIC AND OTHER 



to the structure of nietamorphic rocks of sedimentary origin, and 

 before long to feel the gravest doubts as to the possibility of the 

 great mass of schists associated with the Lizard serpentines being 

 of the same age as the slaty and little-altered Cornish strata, which 

 belong mainly, if not altogether, to the later Palaeozoic period. Each 

 year's experience with the microscope and in other regions did 

 but strengthen this conviction, which of late I have ventured to 

 express frequently ; but it was not until last Easter vacation that I 

 was enabled to revisit the Lizard. In about ten days of hard work 

 I examined with considerable care the coast sections of " hornblende 

 schists," as indicated on Sir H. De la Beche's map, from the Lizard 

 Head to Porthalla on the east, and to Polurrian Cove on the west. 

 During the major part of this time I had the advantage of being 

 accompanied by my friend and former colleague the Rev. E. Hill, 

 Tutor of St. John's College, Cambridge, whose friendly aid I most 

 gratefully acknowledge. A large series of specimens was collected, 

 and evidence obtained, which to my mind is conclusive as to the 

 vast difference in age between the "hornblende schists " and the 

 slaty group. A number of the specimens have subsequently been ex- 

 amined microscopically, and the results are embodied in the following 

 paper, together with some account of two outlying masses of ser- 

 pentine, which I had previously been obliged to leave un visited. 



As on former occasions, Sir H. De la Beche's Geological Memoir 

 of Cornwall and Devon was constantly in my hands, and I cannot 

 forbear again expressing my sense of its thoroughness and value. 

 There are, indeed, some points on which I come to different conclu- 

 sions ; but this is simply because I have had the advantage of using 

 the microscope ; and as regards most of these, I believe that the 

 author had expressed himself more or less doubtfully. Each day's 

 work has but increased my admiration of the genius of the first chief 

 of the British Geological Survey ; and I will venture to say that if he 

 could have had the advantages which we now possess, he would have 

 left little for our generation to do in Cornwall. 



II. Stratigraphy of the Metamorphic Sedimentary Series and its 

 Relation to other rocks. 



In the paper to which I have referred, 1 state that in addition to 

 the "talco-micaceous" schists of De la Beche and the normal horn- 

 blende schists, there is a third group of greyish granitoid rocks, com- 

 posed mainly of quartz and felspar, sometimes almost a quartzite, 

 sometimes simulating a vein-granite, associated with more- horn- 

 blendic, chloritic, earthy, and (as I should have added) micaceous 

 layers. I may refer to pages 885-7 for a sketch of the general 

 petrology of the series ; but on the present occasion, besides supplying 

 many details, I trust to be able to show that there is, in addition 

 to the "talco-micaceous " and the " hornblende-schist " group already 

 recognized, a third or granulitic group. These, however, form but 

 one series, enumerated in ascending order, the first being charac- 

 terized by rather compact dull-green schists, whose exact mineral 

 composition cannot readily be decided in the field, and by brownish 



