1S40.] On the Advancmenf of Geological Science in India. 83 



a rock be found), lamallan or schistous hornblende, an homogenous 

 rock like argillaceous slate. A term for greenstones might be easily- 

 found, to denote the partial admixture or combination of the structure of 

 the hornblende porphyry, without miscalling block stones, green stones^ 

 The term schistous, too, has been most sadly ill used, so that it is diffi- 

 cult to say what it means. If we take argillaceous schist as a type, it 

 means a rock homogenous in structure or in the composition of its parts, 

 which has the property of drawing into laminae. Then we have no 

 other kind of schist, but granite in India, and quartz rock in Norway, 

 which Boase (page 79) tells us "separates into very large plates, several 

 feet in length, and only a few inches in thickness like marble tables.'' 

 Schistous hornblende will be unknown, and mica or common talc may be 

 considered schistous. Gneiss is scaly in structure, in the same way 

 that mica skte is — to this structure the term " foliated" might be ap- 

 plied. The term " porphyry or porphyritic" might be used as Dr. 

 MaccuUoch defines it, " crystals of one mineral embedded in a conti- 

 nuous mass of another.'* We might then say hornblende in felspar por- 

 pliyry— and dropping the proposition '« hornblende felspar porphyry" 

 — then we have ** red in white felspar porphyry" — *' quartz felspar 

 porphyry" — •* felspar quartz porphyry," or crystals of felspar embedded 

 in a paste of compact quartz— all of which are found in India. 



For the last two years, I have been engaged in a geological and mi- 

 neralogical examination of the Salem district, and 1 find many discre- 

 pancies with the theories of European geology, which it will require 

 much labour and assistance to clear up. In Dr. Boase's work, 1 find 

 many points of agreement between the geology of Cornwall, and Dr. 

 MaccuUoch's description of the Scottish Isles, with that of India, 

 which are therefore quite at variance with the prevailing system. 

 In the pursuit of my object, 1 have examined a tract of country in a 

 triangular shape, included between Trichinopoly, Bangalore and Vellore, 

 of which the district of Salem alone contains 7,000 square miles, equal 

 to one-sixth of the area of Great Britain. In this tract I find so many- 

 new minerals, that I have not yet had time to examine them all, and 

 perhaps it may be impossible for a single individual to make all the 

 chemical analysis required. I find that hornblendic granite prevails 

 over all this tract, that it forms a substratum at depths more or less 

 under the surface, the rivers cutting their beds down to this rock. It 

 occurs above the surface generally in rounded masses, heaped together, 

 the rounded form of which has been generally attributed to decomposi- 

 tion, but which is not the case, the shape being original ; in which way 

 it is found embedded in friable gneiss, or kaolin earth, which fill the in- 

 terstices between the blocks, and are washed out on exposure to 

 the weather. Black eranile Chornblende rock or nrimarv PTf-enstonp^. 



