350 



SCIENCE. 



[N. S. Vol. XXI. .Vo. .531. 



quake of large amounts of the quicksand un- 

 derlying the clay, which, when saturated with 

 water, flows almost as readily as water alone. 

 Observation on the ages of trees in the cracks 

 brought out the fact that some fissures were 

 formed a hundred years or more before the 

 recorded quake, while inquiry of the inhabit- 

 ants shows that earthquakes are still of almost 

 annual occurrence and are accompanied by 

 similar but less pronounced phenomena than 

 those accompanying the quake of ISll, indi- 

 cating that the latter was simply an acute 

 stage of a readjustment which has long been 

 going on and is still in progress. 



Some Crystalline Bocks of the San Gabriel 

 Mountains Near Pasadena, California : 

 Ealph Arnold, TTashington, D. C, and 

 A. M. Strong, Independence, California. 

 The San Gabriel Mountains, comprising an 

 area of about twelve hundred square miles, 

 extend for fifty miles in a west-northwesterly 

 direction from Cajon Pass in San Bernardino 

 County, to the Santa Clara Eiver in Los 

 Angeles County. Considerable divergence of 

 opinion regarding the age of the chain has 

 prevailed among previous writers, but it is 

 probable that it received at least the greater 

 part of its elevation during late Eocene or 

 Oligocene time. 



The southern range of the chain, the Sierra 

 Madre, is composed principally of granodiorite 

 and gneiss, with some associated quartz- 

 monzonite and gabbro and intruded aplite, 

 quartz-hornblende-porphyrite and diabase por- 

 phyry. The central portion of the mountains 

 consists of somewhat coarser grained granites 

 and granodiorites with intruded aplite, micro- 

 pegmatite, etc. 



The granites described are of the biotite 

 variety and are found in the central part 

 of the chain. The granodiorites consist of 

 two facies, a fine-grained hornblende-bearing 

 variety from the Sierra Madre and a some- 

 what coarser grained variety containing por- 

 phyritic orthoclase from the central mass. 

 These granodiorites differ from those found 

 in the Sierra ^Nevada of central California 

 by being on the average finer grained and 

 having less quartz, titanite and zircon. 



Gabbro, consisting mostly of hornblende, but 

 also containing a little plagioclase, is found 

 in small masses or dikes throughout the whole 

 area. Aplite is found over the whole region 

 in question, while micropegmatite was found 

 only in the central portion of the chain. 

 Quartz-hornblende-porphyrite and diabase por- 

 phyiy occur in dikes in the southern range. 

 Of the metamorphic rocks, hornblende-diorite- 

 gneiss is by far the commonest. It and some 

 biotite-granite-gneiss are associated with the 

 granodiorites and quartz-monzonites of the 

 Sierra Madre. Hornblende-schist and gar- 

 netiferous schist, found by the writers only 

 in the southern range, complete the list of 

 crystalline rocks described. 

 The Question of the Origin of the Xatural 



Mounds of Louisiana: A. C. Yeatch. 



Of the many theories of origin suggested 

 for these mounds three deserve the most care- 

 ful attention : (1) the spring and g'as vent 

 theory, (2) the dune theory and (3) the ant 

 hill theory. 



In the spring and gas vent theory it is 

 argued that the gas produced by the decay of 

 the large amount of vegetable matter buried in 

 the coastal plain strata has, with the artesian 

 water associated with it, brought to the sur- 

 face fine sand and built up low cones. Small 

 cones are now forming in this manner at 

 many points in the coastal plain, and they 

 were pointed to as proving this hypothesis. 

 The fatal objection to this theory is that en- 

 tirely identical mounds are found in Indian 

 Territory on flat plains underlaid by highly 

 inclined carboniferous shales and sandstones, 

 where the substructure clearly lacks the ele- 

 ments required by this hypothesis. 



The dune theory is based on the resemblance 

 of these mounds to the low dunes which col- 

 lect in the semi-arid region of the west about 

 clumps of low vegetation. The objection to 

 this theory is the great irregularity of wind- 

 made features and the very notable uniformity 

 in size and exact resemblance one to another 

 of these natural mounds of the south central 

 United States over an area at least 300 miles 

 wide and 500 miles long. It would seem that 

 in so large an area a wind origin would in- 

 volve a greater variation in size than has been 



