TENDAU— TRANSITION. 117 



The beds contain fossils having general affinities to those of the 

 Umia beds of Cutch. They are also correlated with the Chikiala 

 sandstones of the Upper Godavari valley. 



Tonbo beds. — Name used by P. N. Datta (Director's General Report 

 for 1899-1900, 99, 116) for the limestone beds forming the west- 

 ern foot-hills of the Shan plateau. The beds were regarded as 

 Lower Silurian in age. Subsequent work of T. H. D. La Touche 

 (Director's General Report for 1906, Rec, Geol. Surv., Ind., 

 XXXV, 52, 1907) resulted in the discovery of Fusulina and other 

 forms, described by C. Diener (Pal. hid., New Ser. ; Vol. Ill, Mem. 

 No. i) indicating a Permo-Carboniferous age. The name has 

 been discarded in favour of Plateau Limestone (q. v.). 



Tons series. — Name proposed by E. Vredenburg (Rec, Geol. Surv., 

 Ind., XXXIII, 258, 1906) to include the old Rewa and Kaimur 

 stages of the Vindhyan system. From the Tons river, which 

 drains the broad table-land in Central India, constituted by the 

 Kaimur and Rewa rocks. The Tons series and Son series (old 

 Lower Vindhyan) are thus united to make up the Ken sub-system, 

 or lower main division of the Vindhyan system. 



Transition systems. — The term Transition was applied first by Werner 

 to the sedimentary rocks which were regarded as older than 

 the fossiliferous or Secondary and younger than the hypogene 

 gneisses and granites or Primitive rocks of Lehman's classifi- 

 cation. Long before the Geological Survey of India was found ■ 

 ed, the work commenced by Murchison and Sedgwick in 1831 

 resulted in the recognition of fossiliferous systems among the so- 

 called Transitions of Great Britain. The term thus became 

 curtailed in its stratigraphical application, and in India was used 

 to cover the older of the unfossiliferous systems in the Peninsula 

 which were found to occupy a position intermediate between 

 the Vindhyans and the Gneissic or Metamorphic (Man. Geol. 

 Ind., 1879, pp. xiii, xix, 3, 28). The transitions thus included 

 the Gwaliors, Cuddapahs and Kaladgis in the upper division, 

 and the Champaners, Aravallis and what were afterwards called 

 the Dharwars in the lower division. The Kurnools and Lower 

 Vindhyans (Semri) were thus placed in the higher system as 

 Vindhyans. In the 2nd Edition of the Manual, published in 1893, 

 R. D. Oldham (chap. Ill) included in the Transitions the dis- 

 tinctly foliated formations like the Dharwars, the Aravallis, the 

 Champaners and the similar schistose and semi-schistose rocks 



