ABSTRACTS AND DISCUSSIONS OF PAPERS 1.19 



finer calcareous material have generally been entirely removed by leaching; 

 where the drift is thicker than 4 or 5 feet, it is highly calcareous below the 

 leached zone. At one place the gumbo bed outcropped in a slope about 50 

 feet below the top of the ridge. 



It thus appears that there is clearly a post-Kansan till in northeastern Iowa. 

 It is older than the Wisconsin and seems to be distinctly younger than the 

 Illinoian, The loess, which is largely absent or very thin in the Iowan area, 

 mantles the weathered and eroded surface of the Illinoian drift as it does that 

 of the Kansan. A similar gumbo bed was found in western Iowa between 

 two drift sheets, apparently the Kansan and Nebraskan, but this need not be 

 discussed at this time. 



Mr. Frank Leverett stated that in case the gumbo is a derivative from 

 boulder clay microscopical examination should bring to light insoluble min- 

 erals, aside from siliceous rocks, that were combined to make up the rocks 

 which are common in the boulder clay, but have not been found preserved in 

 coarse fragments in the gumbo. The interpretation by Professor Kay seems 

 at best but tentative and will need to be tested by such lines of evidence as 

 are now under investigation, so that a year hence we may know better the 

 value of the interpretation. So far as Mr. Leverett's personal observations 

 have gone, there seems lacking the transition zone between boulder clay and 

 gumbo which one would expect to find if the gumbo is a derivative from 

 boulder clay. Usually less than a foot space will take one from typical 

 boulder clay into typical gumbo, and one's first impression is that the gumbo 

 has been deposited on the boulder clay as a distinct bed. 



Mr. Charles E. Decker : I have seen examples of the gumbo which Professor 

 Jvay describes at the Survey Office in Washington. These samples are very 

 much like a thoroughly leached clay that occurs in connection with the oldest 

 drift in northwestern Pennsylvania at Franklin and Oil City. However, there 

 are larger fragments of rock in the clay at those localities than in the speci- 

 mens of gumbo. 



TRIASSIC ROCKS OF ALASKA 

 BY GEORGE C. MARTIN 



(Abstract) 



Triassic rocks, including over 5,000 feet of limestones and shales with highly 

 characteristic marine Upper Triassic (Karnic and Noric) faunas, are now 

 known to be widely distributed in Alaska. The Middle and Lower Triassic 

 are represented by a single known occurrence of marine Middle Triassic 

 shales and possibly also by volcanic and metamorphic beds. The more impor- 

 tant Alaskan Triassic sections were described and correlated. Correlations 

 were also suggested with the Triassic occurrences in British Columbia, as 

 well as with the better known Triassic sections in California and other parts 

 of the world. An outline was given of the events of Triassic time in the 

 northwestern part of America. 



Presented in abstract extemporaneously. 



