44 HOLLAND AND TIPPER : INDIAN GEOLOC4ICAL TERMINOLOGY. 



Disang series.— Named by F. R. Mallet (Mem., Geol. Surv., Ind., XII, 

 286, 1876) from the Disang river in North-East Assam. Regarded 

 on indirect evidence as older than the local Tertiary Coal Measures, 

 and probably equivalent to the similar Negrais series of the 

 Arakan Yoma. Similar rocks were noticed by F. H. Smith, 

 [Mem., Geol. Surv., Ind., XXVIII, 91, 1898) in the MiMr hills to 

 be overlying the Nummulitics, and he suggested consequently 

 that the Disangs also are post-Nummulitic. 



Doab Series. — Composed mainly of volcanic ejectamenta interbedded 

 with shales, sandstones, and, locally, conglomerates, unconform- 

 able overlying Fusulina limestones, but covered apparently con- 

 formably by the plant-bearing Saighan series of Jurassic age. In 

 the absence of fossils the stratigraphical relations are taken to 

 indicate a probable Trias-Jura age. On account of its exposure 

 near the Doab-i-Mekhzarin (35° 17' ; 68° 2'), or junction of the 

 Kahmard and Saighan rivers in Eastern Afghanistan, it has been 

 named the Doab series by H. H. Hayden (Mem., Geol. Surv., Ind., 

 XXXIX, 28, 1911). 



Dolomite series. — One of TV. Waagen's divisions of the Ceralite beds 

 (q.v.) of the Punjab Salt Range. 



" Dome " gneiss. — A descriptive term adopted for a type of supposed 

 gneiss tvpically developed in the gneissic area of Northern Bengal, 

 and so called from its weathering into huge hemispherical or 

 ellipsoidal masses of bare rock, the only divisional planes being 

 concentric layers of exfoliation. The hills are often several 

 hundred feet high and form a very peculiar object in the land- 

 scape. Foliation is always more or less traceable, and in every 

 respect of texture and composition the rock is the same as that 

 of the thin bands alternating with schists in the adjoining ground. 

 Both are often porphyritic, the dome gneiss generally so, contain- 

 ing large rounded felspar crystals. The earliest description is 

 by°H. B. Medlicott (Rec, Geol. Surv., Ind., Vol. II, 42, 1868). In 

 a more recent description, T. H. Holland (Mem., Geol. Surv., Ind., 

 Vol. XXXIV, 47, 1902) shows that the rock is a granitite, being 

 composed of quartz, microchne, with smaller quantities of oligo- 

 clase, biotite, hornblende, accessory sphene, etc. The rock 

 further resembles undoubtedly eruptive granites in the posses- 

 sion of autoliths due to local concentration of the ferromagnesian 

 minerals, contemporaneous coarse-grained veins, xenolitbs of 

 quartzite and a well-marked zone due to contact action near its 



