214 E. HILL ANT) T. G. BONNEY OK THE 



be traced some fifty yards. We have several times observed con- 

 siderable portions of the old surface of the syenite exposed near 

 here; it is very irregular, the projections being slightly ronnded, 

 but not so as to suggest glacial action. The Sheet-Hedges-Wood 

 pit is a large excavation further north in the same mass; both 

 varieties of the rock are found here, and the differences, if any, are 

 so slight that no description is needed. There is a small greenstone 

 dyke in this pit. The general character of the syenite all over this 

 district, and in the hill at Markfield, where there are large excava- 

 tions, is so similar that details would be only repetition ; possibly 

 an experienced quarryrnan might recognize the rock of his own pit, 

 but in many cases we certainly could not undertake it. We have 

 not, however, observed the finer variety of the syenite at Markfield, 

 but have seen it in Bradgate Park, in the stream a little below the 

 lowest fishpond, near to which there is also a greenstone dyke. In 

 one of the Markfield pits there used to be a considerable vein of 

 reddish calcite. 



At the southern end of the Cliff Hill mass a large pit is worked. 

 The texture of the rock is very like that of Markfield, but it has a 

 slightly more decomposed aspect. There is more of the greenish- 

 coloured felspar, and the red of the rest is paler. We did not see 

 any dykes in this pit. 



The rock is not quarried at Hammercliff, and so it is more diffi- 

 cult to obtain good specimens. In general it appears to be a little 

 more finely crystalline than at Markfield, with a duller aspect, and 

 an approach to the less definite crystalline structure which charac- 

 terizes the northern syenites. A rather compact variety, of a toler- 

 ably uniform dull-green colour, is also found here. 



Microscopic Structure of the Southern Syenite. — Slices of the coarser 

 variety of this rock have been examined from the Old Quarry 

 and the Pool Quarry, Groby, from Markfield, Bradgate-House 

 Wood, and Cliff Hill. They resemble one another so closely that a 

 detailed description of each is needless.. The rock consists of felspar, 

 hornblende, quartz, apatite, and oxide of iron, with various secondary 

 products, as epidote, viridite, and chlorite. The felspar chiefly 

 occurs in tolerably regular crystals, polygonal in section, approach- 

 ing oblongs ; there is a fair quantity of plagioclase as well as ortho- 

 clase. The former exhibits the usual parallel structure and sometimes 

 zonal banding*. The felspar is often much decomposed, partly filled 

 with brown dust, partly with minute granules. With crossed Nicols the 



* MM. Poussin and Eenard observe this structure in the oligoclase of the 

 Quenastdiorite(Mem. sur les roch.es plutoniennes, &c. p. 29) ; probably the fel- 

 spar here also is oligoclase. A specimen of the Quenast rock, kindly given to me 

 by Prof. Morris while this paper was passing through the press, has a general 

 resemblance to that from Grarendon (p. 217), except that it is lighter in colour 

 and free quartz is conspicuous. Microscopic examination shows it to be nearer 

 to the Narborough or Enderby rocks described below, the ground-mass being 

 microcrystalline. It is, however, closely related lithologically to our Oharnwood 

 group of igneous rocks. This is remarkable, because Prof. Eenard, in examining 

 my collection of the more altered sedimentary rocks, was struck with their close 

 resemblance to some of the " porphyroids " of the Ardennes. — T. Gr. B. 



