4 PEOF. T. G. BONNET ON THE HOENBLENDIC AND OTHEB 



The general dip here is between K".E. and N.N.E. At low tide, a 

 small intrusive mass of a porphyritic diabase * only exposed for a few 

 yards, and rarely more than one yard in thickness, can be seen. It 

 is the only igneous rock which I have detected in this group. 



The next cove, bounded on the east by the great headland on 

 which stands the lighthouse, marks the junction of the micaceous 

 with the hornblendic series. This is undoubtedly a faulted one ; 

 but I believe the displacement to be but slight, and after more than 

 one examination I retain the opinion previously formed that there 

 is no real stratigraphical break between the two. The headland 

 consists of hornblende schist, the beds of which dip gently under 

 the lighthouse ; and the same rock is exposed a short distance inland 

 on the road from Lizard Town to Polpeor Cove. From beneath the 

 lighthouse to the Bumble Eock the crags are formed of normal horn- 

 blende schist, with fairly well-marked bedding, which, with minor 

 rolling, dips gently to the E.N.E. 



Beyond the Bumble comes Housel Bay, with its fine cliffs. Here 

 the beds of the hornblendic series, which are slightly more massive 

 and epidotic near the little rift at its head, appear to form a very 

 slight synclinal followed by an anticlinal ; but the strike continues 

 W.N.W. to E.S.E., and we seem to rise a little as we proceed in 

 an E.N.E. direction, so that on the whole the beds on the Bumble 

 appear to underlie those of Penolver Point. On the eastern side 

 of this headland the beds are beautifully banded, consisting of dark 

 hornblende and whitish felspar (which weathers a light brown 

 colour), and afford indications of false bedding. The gentle rollings 

 continue to Beast Point, where there is rather distinct lenticular 

 bedding, but on the whole there appears to be a gradual dip to 

 E.N.E. At the Point itself the dip is sharper, perhaps 30°, but 

 there is much contortion. The coast-line now has a general trend 

 to the north, and hence to Hot Point the variable bedding and the 

 disturbances continue. At the base of the latter locality the beds 

 seem to be doubled up, the strike of the roll being N.N.W. Here- 

 abouts the structure of the rock is most interesting. Lenticular 

 bedding is frequent, there are some of the most remarkable instances 

 of false bedding on a small scale that I have ever seen (PL I. fig. 2), 

 and indications here and there of a kind of ripple-drift. It is impos- 

 sible to resist the conclusion that, notwithstanding the great amount 

 of metamorphism, we have here a record of true " current-bedding " 

 (whether by water or by wind) in the original constituents of the 

 rock. 



*!Maeroscopically it exhibits a rather compact dark grey ground-mass, in which 

 are scattered numerous elongated crystals of a whitish waxy-looking felspar, 

 up to about "5" in length. Microscopically the ground-mass consists of a fel- 

 spathic mineral full of secondary microliths, with the original structure quite 

 obscured, and of hornblende, often occurring in rather distinct prisms clustered 

 together side by side, besides some grains of iron peroxide. The aspect of the 

 hornblende suggests that it is of secondary origin. The larger crystals of felspar 

 are also much decomposed, and all that can positively be said is that the fel- 

 spar is a plagioclase. I regard the rock as a hornblendic diabase, rather than 

 a true diorite. 



