PALEOZOIC AND MESOZOIC BORDER-LINE 5 I 3 



account was taken of conditions of formation, and this has led 

 to endless difficulties in correlation. The Upper Carboniferous 

 was based entirely on lacustrine deposits, and the identification 

 of its marine equivalent is still making trouble for geologists. 

 The Permian was based on a basin deposit, partly lacustrine and 

 partly of brackish water origin, and the recognition of its purel}^ 

 marine types has caused much controversy in Europe and Amer- 

 ica. The Trias was based at first entirely on the deposits of 

 the Germanic inland sea, and only recently has any uniformity 

 been attained in its correlation and nomenclature. 



The greater divisions are now all named, and there is no room 

 for new systems, all geologic time, and possibly something over, 

 being taken up by those already defined. But because the first 

 naming of geologic divisions was based on unconformities, 

 which represented erosion intervals and consequent gaps in the 

 record, further exploration must necessarily bring to light some- 

 where in the world passage beds between the artificial systems. 

 What rules then shall be followed in the correlation of these 

 passage-beds, or new formations ? If the new formations are 

 shown to be the homotaxial equivalents of parts of systems 

 already defined, there can be no question, for faunal or lithologic 

 differences cannot be taken in account in different provinces or 

 regions. 



If the new formation, however, lies between two systems, one 

 of which is sharply defined and the other described only vaguely, 

 as including the beds below or above the one with definite 

 boundaries, then the passage-beds must naturally be assigned to 

 the system with a flexible margin. 



If both the bordering systems should be definitely bounded, 

 or if neither should be, then one or the other must be stretched 

 to take in the passage-beds, and the assignment will be based 

 on paleontologic relationship to one or the other. But if this 

 relationship should be no closer to one than the other, then prior- 

 ity of assignment would have to decide on the nomenclature of 

 the doubtful beds. 



The geologists of India have for many years recognized that 



