152 RECORDS 



Dr. E. 0. Hovey gave a brief summary of the chief facts 

 known in regard to the formation of the Black Hills, describing 

 first the most striking features of the great Red valley, which 

 has been formed by the comparatively rapid erosion of the Tri- 

 assic beds, which are softer than the Permian limestone on the 

 one side, and the Jurassic sandstones on the other. The Tri- 

 assic beds are very variable in texture, consisting of clay-, 

 sand- and gravel-rock ; they show much strong cross-bedding, 

 being evidently a shore deposit. They seem to have suffered 

 much from local slipping, making a close estimate of their 

 thickness hard to give. They are entirely destitute of animal 

 remains. The Jural sic beds are separated from the Red beds 

 by an unconformity due to erosion. They consist of argilla- 

 ceous and calcareous shales, limestones and sandstones, but they 

 are very variable in composition. Some of the layers contain 

 abundant fossils, forty- six species having been reported from 

 the formation. Apparently there are ten or twelve new species 

 in the material collected by the author for the American Mu- 

 seum last summer (1901). The upper boundary of the Jurassic 

 is still a mooted question, the beds running conformably up into 

 undoubtedly Cretaceous, with no invertebrate fossils for hun- 

 dreds of feet. The paper was discussed by Professors Steven- 

 son and Dodge and Dr. Grabau. 



Dr. Julien, in his paper on Erosion by Flying Sand on the 

 Beaches of Cape Cod, described the physical characteristics of 

 the beach sand of Cape Cod, and showed them to be in gen- 

 eral derived from the Tertiary formation and from the glacial 

 sands and gravels. The motion of the sands is from the west 

 along the south shore, and from the north down the east and 

 west sides of the "forearm" of the cape. The sand movement 

 under the influence of the wind is extensive, and many results 

 of erosion by moving sand are seen in the wearing of cliffs and 

 in the pitted surfaces of the pebbles on the beaches. 



The author showed also that the sand grains suspended in the 

 air are subjected to rapid erosion from mutual impact, and thus 

 that sand particles too small to be eroded in water are much 

 comminuted when dry, and set in motion in the air. The fine 



