TITLES AND ABSTRACTS OF PAPERS /O 



GLACIAL LAKES OF SAGINAW BASIN IN RELATION TO UPLIFT 

 BY FRANK LEVERETT 



(Ahstrad) 



By the aid of topographic maps with 5-foot contours, it has been found that 

 the liiglier beachesi — Saginaw and Arkona — in tlie Saginaw Basin have been 

 uplifted northward, but that the low beach of Lake Warren, formed at a later 

 time, has not been uplifted in this area. It is, however, tilted in neighboring 

 ports of Michigan to the north. The area of uplift thus became reduced on 

 the south during the Glacial epoch. Similar phenomena have been observed 

 in the Huron-Erie Basin and are discussed by Taylor in Monograph LIII, 

 United States Geological Survey. 



Presented in full extemporaneously. 



^MECHANICS OF LACCOLITHIC INTRUSION 

 BY CHARLES R. KEYES 



{Abstract) 



Between the two extreme views concerning the genesis of laccolithic moun- 

 tains, between the idea of an easily floated prism of strata that expands into 

 a symmetrical, dome-shaped earth-blister, and the notion that the phenomenon 

 is a mechanical impossibility, there now develops midway a strictly tectonic 

 conception which, although making improbable the one and perfectly invali- 

 dating the other, is amply supported by recent wide observation, and withal is 

 mathematically sound. It turns out that the genetic impetus in its nature is 

 dominantly orogenic rather than simply hydrostatic. 



In the Sierra del Oro, or Gold Mountains, of New Mexico, of which the Ortiz 

 group is the best known, the structural relationships of laccolithic intrusion 

 are especially well displayed. The ideal form of the laccolithic mass is shown 

 to be not a symmetrical lens, but a wedge-shaped body in which a fault-plane 

 constitutes the flat, thick base. 



A laccolithic mountain is not fortuitously located. In order that a laccolith 

 be produced, rather than any other form of volcanic manifestation, it seems 

 that the intrusive mass must have a particular tectonic setting. Profound 

 faulting is one of the prime factors. Another is orographic flexing by which 

 the rigidity of certain arching strata potentially carries or largely sustains 

 the load of superincumbent beds. Probably the unusually high viscosity of 

 acidic magmas has an important, but as yet uncalculated, influence on events. 

 The four laccoliths of the Sierra del Oro are situated at equidistant points, 

 where recently formed folds intersect at an angle of 45° a notable line of 

 ancient displacement. Like circumstances may obtain for all laccoliths. 



A laccolith is not a locally thickened sill. The two masses are formed under 

 entirely different physical and tectonic conditions. They are genetically dis- 

 tinct and perfectly unrelated. 



Read bv title in the absence of the author. 



