Ja.nuaky 18, 1895.] 



SCIENCE. 



59 



tions is a matter of great ditlieulty, if not 

 impossibility. Tlie great number of the 

 faults, and tlie consequent small size of the 

 various faulted blocks, are striking facts. 



In discussion C. 1). Walcott showed how 

 these faults had led Professor J. ilarcou to 

 believe that he had discovered colonies of 

 Trenton fossils in rocks of the Potsdam. 



5. The Formation of Lake-basins hi/ ]Vin(l. 

 G. K. Gilbert, Washington, D. C. 



The paper described the formation of ba- 

 sins in the arid regions of the West, by the 

 erosive action of wind-blown .sand upon a 

 shale devoid of ACgetation. In time they 

 became tilled with water and formed small 

 lakes. 



6. The Tepee Bti/tes. (i. K. Gilbert and 

 F. P. Gulliver. 



The paper was read by Mr. Gulliver and 

 described a series of conical buttes west of 

 Pueblo, Col. They consist of Pierre shales, 

 surrounding cores of limestone formed of 

 shells of Lucina. It is supposed that as the 

 shales were deposited, a colony of lucinas 

 established themselves and grew upward 

 pari passu, foi-ming a conical or columnar 

 deposit of limestone, whose greater resist- 

 ance to erosion has left the buttes in relief. 



7. Jlemarks on the Geology of Arizona and 

 Sonora. "W J McGee, of Washington. 

 The arid region was described as consist- 

 ing of north and south mountain ranges 

 with wide valleys between. In Arizona the 

 surface is largely of volcanic rock, in Sonora 

 of Mesozoic limestone. The rivers have 

 definite courses and water in the moun- 

 tains, but in the valleys they are lost by 

 evaporation and absorption before the ocean 

 is reached. Their valleys were transverse 

 to the mountains and larger vallej's because 

 of the general southwesterly dip of the 

 rocks. Buttes near the Gulf of California 

 show slight talus, which fact gives good 

 ground for thinking that the gulf has stood 

 at an altitude, as regards the land, several 



hundred feet above its present level in re- 

 cent geological time, or, in other words, that 

 the land has been depressed by that amount. 



8, Geology of the Highicood Mountains, Mon- 

 tana. Walter H. Weed, AVashington, 

 D. C, and Louis V. Pirssox, Xew 

 Haven, Conn. 



On account of the illness of Mr. Weed this 

 paper was not read. 



9, Genesis and Structure of the Ozark 

 Uplift. Charles R. Keyes, Des Moines, 

 Iowa. 



On account of the author's al)sence the 

 paper was not read. 



10, The Geographical Evolution of Cuba. 

 J. W. Spencer, Washington, D. C, 



The description of the physical geography 

 of Cuba and of the adjacent submerged 

 banks was given. Exclusive of a few areas 

 locall}' older, the apparent basement is com- 

 j)0sed of volcanic rocks of Cretaceous or 

 slightly earlier date. These are succeeded 

 by fossiliferous Cretaceous sands, etc., and 

 limestone greatly disturbed. The Eocene 

 and Miocene deposits form a physical unit, 

 and are composed mostly of limestone 

 having a thickness of from 1,900 to 2,100 

 feet. The Pliocene period was mostly one 

 of high elevation, accompanied by a very 

 great erosion. At the close of the Pliocene 

 period the Matanzas subsidence depressed 

 the island so as to leave only a few small 

 islets, and permit of the accumulation of 

 about 150 feet of limestones. Then followed 

 the great Pleistocene elevation with the 

 excavation of great vallej's, the lower por- 

 tions of which are now Qords reaching in 

 one case at least to 7,000 feet in depth be- 

 fore Joining the sea bej'ond. The elevation 

 was followed by the Zapata subsidence, re- 

 ducing the island to smaller proportions 

 than to-day, and permitting the accumu- 

 lation of the loams and gravels like the 

 Columbia of the continent. The subs((|uent 

 minor undulations are also noted, as shown 



