PALEONTOLOGY. 457 



in the character of tufas so far separated in time is to be expected, 

 since (at least theoretically) temperature, salinity, and the character 

 of the conditioning algal life must be the slightly changing factors 

 of deposition. Extension of this trend or shore-line is indicated by 

 tufas like those of the Como Bluff region, also said to occur about 

 5 to 13 miles further east (in the southwestern part of township 25). 

 The forms are darker, rather smaller, harder, and more siliceous. 

 The polished pebbles, often of 5 or 6 pounds in weight, have been 

 seen in the Lakota in great numbers, and the data of these occurrences 

 should be carefully assembled. Such pebbles could and must often 

 have been swallowed by larger reptiles, but in view of widespread 

 occurrence and varying character the so-called ''gastroliths" must be 

 limited to the isolated polished-pebble groups actually noted in rib 

 or thoracic association, instances of which are of more or less authen- 

 tic record. The polished shore-line pebbles are, then, most widely 

 distributed in the Lakota, although first reported from a sauropod 

 association in the Como. In the latter formation they may also 

 prove abundant, as it is stated (by Knowlton) that in the Big Horn 

 Basin, 5 miles west by north of Ten Sleep, the varicolored beds (Como) 

 are in many places characterized by the gastroliths. Two cycadeoids, 

 Zamites arcticus Heer and Nilssonia nigricollensis Wieland, occur in 

 this locality. They also may accord with a very dry climate. 



Altogether, the remarkably curious evidence bearing on the climate 

 of the northwestern Lower Cretaceous seems to have long escaped 

 notice. Moreover, the assemblage of data becomes far more im- 

 portant than can any attempt to reach at once a fixed or set view. 

 There is the promise that much more can yet be learned of the cli- 

 matic environments indicated by the Como and Lakota plants, even 

 though the number of recovered leaf-imprint species should remain 

 small. 



During the present year the private laboratory unit at ''Anawan" 

 (near the Oyster River, Connecticut), mentioned in Year Book No. 

 13, has been further equipped and much used. The only outside 

 cooperation to record is that generously given by the Harvey & Lewis 

 Co., opticians of New Haven. Their men, skilled in the art of 

 accurate lens-grinding, have taken interest in the art of thin-section 

 cutting and have helped materially in the preparation of sections 

 fulfilling the fine requirements set forth above. 



