510 



Dr. L. Leigh Fermor — What is Laterite ? 



quartz sand, or by the admixture of detritus from true laterites 

 with quartz and argillaceous detritus from gneissic or granitic rocks. 

 The correct name for these rocks will be, then, detrital laterite or 

 lateritite. 



The Ponri Hill Later itic Lithomarges. — As another example, I may 

 refer to a series of superficial rocks found at Ponri Hill in the Jabalpur 

 district, which I hope to describe later in the Records of the Geological 

 Survey of India under the heading of lateritic lithomarges. On first 

 examining this hill, I thought it was an occurrence of very aluminous 

 laterite, and, consequently, took for analysis two bulk samples, 

 representing the two principal varieties of the rock. I was much 

 surprised, when the results of the analyses came to hand some three 

 or four years ago, to see that the samples contained, respectively, 

 24-60 per cent and 31-90 per cent of Si 3 ; but I at once decided 

 that, in spite of their superficial resemblance to true laterite, both 

 in physical appearance and in the ease with which they could be cut 

 into blocks for building purposes, these rocks could not be regarded as 

 laterites. Closer inspection was sufficient to show that the ground- 

 mass of the rock consisted of a compact, somewhat horny, substance 

 corresponding to the litbomarge, the presence of which was indicated 

 by the analyses, and that the rock consisted of patches of lateritic 

 material distributed through a lithomargic base. The analyses are 

 given below, together with that of a third example, in this case 

 a hand-specimen of a white pisolitic rock, collected by Dr. Maclaren 

 at Mendil near Talevadi in the Belgaum district of the Bombay 

 Presidency. The Mendil specimen was forwarded by me to 

 Messrs. J. and PL S. Pattinson of Newcastle for analysis with my 

 samples of manganese-ore, whilst I was Curator of the Geological 

 Museum. Dr. Maclaren and I were both under the impression that 

 this specimen was a piece of very high-grade bauxite, and had not 

 the slightest suspicion of its siliceous nature. As will be seen from 

 the following table, in which are given also the analyses of the 

 samples from Ponri Hill, the Mendil specimen contains a very large 

 amount of silica : — 



