CHAPTER VI. 



ORDOVICIAN SYSTEM. 



In studying the geology of an area that has not been previously 

 surveyed it is convenient, and in most cases 



Nomenclature. , , , . , , 



absolutely necessary, to give local names to 

 the formations met with ; and the names that naturally occur to 

 the surveyor are those of villages, hills, rivers, etc., in the vicinity 

 of which he first meets with that particular formation. Moreover, 

 if two observers are working in the same region, and are, as so often 

 happens in this country, unable to communicate with each other, differ- 

 ent names are apt to be given to the same formation, especially when the 

 character of the country is such that it is difficult to correlate one 

 set of observations with another by mere description of the rocks 

 which each individual has met with. It is for this reason that so 

 many discrepancies will be found in the accounts of the geology 

 of the Shan States originally published in the General Report of 

 the Geological Survey of India for 1899-1900 by Mr. Middlemiss, 

 Mr. Datta, and myself. Indeed, so widely did the interpretation 

 that each of us put upon the observations we had made differ 

 from each other, that it was thought advisable at the time to pub- 

 lish each description separately, leaving it to future investigation 

 to reconcile the points of difference. The names given by Dr. 

 Noetling also, during his rapid traverse of the same ground in 

 1890, do not correspond with ours. For instance, his 1 Pyintha 

 limestones,' of lower Silurian age, were found to include beds belong- 

 ing to both the Ordovician and Silurian systems, and were sub- 

 divided by me into the Zebingyi beds (upper Silurian), Nyaungbaw 

 and Naungkangyi beds (Ordovician). Also his ' Mandalay lime- 

 stones,' which he placed beneath the Pyintha limestone, have since 

 been found to include strata of Devonian age. 



As the survey of such a countiy proceeds, however, some of the 

 , names at first given to the formations are 



Correlation with Euro- » r » . ~ . , 



pcan systems. found to be inconvenient, or not sufficiently 



comprehensive ; others are rejected, as the 

 identity of the strata becomes apparent, to which at first separate 

 names had been given in different localities ; while, as the collec- 

 tions of fossils expand, and the genera and species to which they 

 belong are determined, it becomes possible to correlate the forma- 



