162 T. H. Holland — Petrology of Job Charnock's Tombstone. [No. 3, 



The Petrology of Job Charnock's Tombstone, — By Thomas H. Holland, 

 A.R.C.S., F.G.S., Geological Survey of India. 



[Received August 29th, Read November 1st. J 



At the suggestion of the Rev. H. B. Hyde, I recently examined 

 the tombstone preserved in the ' Oharnock Mausoleum,' St. John's 

 Churchyard, to the memory of Job Charnock.* Apart from its historic 

 interest, the rock itself, being of a type hitherto undescribed, is of 

 sufficient scientific value to call for a description. 



The abundance of blue quartz, the occasional crystals of garnet, 

 the black, and sometimes bronzy-looking, pyroxene, and the cleavage 

 faces of the felspars are characters which are at once striking features 

 in the baud-specimen. 



Under the microscope, the rock is seen to be granitic in structure ; 

 that is, it is perfectly crystalline throughout, with the crystals mutu- 

 ally interlocked, and the intergrowth so perfect that in places a beauti- 

 ful micro-pegmatitic structure results. The following minerals can 

 be identified (1), Quartz. (2), Orthoclase (Microcline). (3), Plagio- 

 clase. (4), Hypersthene. (5), Garnet, and (6), Magnetite. 



(1.) The QUARTZ-CRYSTALS are crowded with minute acicu- 

 lar inclusions, the structure of which cannot be made out with the micros- 

 cope ; they are arranged without discoverable regularity : and are pro- 

 bably the cause of the blue colour seen in hand-specimens. Blue 

 quartz-crystals have been noticed before in granites and granitites, as 

 in that from Rumburg in Sweden. 



(2). ORTHOCLASE and MICROCLINE. Most of the potash- 

 felspars show the remarkable and unmistakable microcline structure. 

 Occasionally also the orthoclase is seen presenting the "streifige " appear- 

 ance due to regularly arranged intergrowths with a plagioclase, giving 

 rise to the structure described by Becke as micro-perthitic. To prove 

 the identity of this felspar I have isolated crystals having a specific 

 gravity of 2 - 59, and examined them chemically by Szabo's method. 



(3). PLAGIOCLASE occurs only in small quatvtities. The isolated 

 crystals show the characteristic twinning, with extinction-angles ap- 

 proaching those of oligoclase. 



(4). HYPERSTHENE occurs, not in large quantities, but present- 

 ing its characteristic pleochroism and straight extinction. The presence 

 of this mineral is a feature of exceptional interest from the fact that, so 

 far as I am aware, a hyperstheue-granite has never before been record- 



* Job Charnock died in 1693, and the tombstone was erected about two years 

 later. 



