TITLES AND ABSTRACTS OF PAPERS 91 



work are independent of and with no relation to the higher levels of the Hud- 

 son estuary. 



The evidence of the continuous high-level shore phenomena throughout the 

 Hudson-Champlain, the Saint Lawrence, Connecticut, and all other deep val- 

 leys of northeastern America (see Bulletin of the Geological Society of Amer- 

 ica, volume 29, pages 187-234), is proof of postglacial marine submergence. 

 The stream-erosion features at Mechanicsville are carvings in the estuary de- 

 posits, produced while the region was rising out of the standing waters. That 

 the so-called "Lake Albany" waters were estuarine and not glacial has been 

 shown in the Bulletin, volume 28, pages 291-292. 



Professor Stollek said: I defer to Professor Fairchild's extended study of 

 glacial history in its broader aspects. Without entering on a controversy as 

 to any of the larger questions, I would ask Professor Fairchild to state how he 

 accounts for the topographic features I have called attention to in my paper. 



May I ask Professor Fairchild whether he is able to understand the terrace 

 forms at Mechanicsville which I have described as erosion terraces as due to 

 currents flowing in the Hudson Valley waters? 



SUBTERRANEAN ''CHALK-STREAMS" OF NORTHERN FRANCE 

 BY EDWARD MOORE BURWASH 



(Ahstract) 



1. British base in France corresponds largely with portion of French coast 

 underlain by chalk — their lines of communication and battle-front during the 

 war mainly on this formation. 



2. Minor streams of this area, and many tributaries of the major ones, flow 

 subterraneously through the chalk, under dry valleys. 



3. Peculiarities of these valleys: (1) flat bottoms; (2) graben in the level 

 flows; (3) fault-scarps on slopes parallel to the valley. 



4. Relation of these facts to one another : 



(1) Pattern of valleys erosional, not structural. 



(2) Course of streams under valleys irregular — traceable by graben 



(3) Fault-scarps sometimes on one slope of the valley, but absent or 

 the opposite side. 



(4) Streams sometimes under the side sloi)es of the valley. 



5. Explanation. Meandering of underground streams — removing layers of 

 chalk and allowing slumping of blocks above. 



6. Suggested history of such streams. 



7. Their importance as source of pure water. 



Read bv title in the absence of the author. 



RELATIVE EFFICIENCY OF NORMATIVE AND MODAL CLASSIFICATIONS OF 



IGNEOUS ROCKS 



BY EDWARD B. MATHEWS 



{Abstract) 



Among the chief outstanding differences in classifications of igneous rocks- 

 are the bases underlying them, and among these perhaps the widest divergence 



