May 1, 1896.] 



SCIENCE. 



653 



northwestern corner to over 4,000 feet in 

 the northeastern corner. The topography 

 is characterized by a number of parallel 

 ridges, running in a north-northwest direc- 

 tion. The northeastern part has more 

 the character of an irregular and undulating 

 table-land. Through the ridges and the 

 plateaus the watercourses have cut deep 

 and narrow canyons. The Yuba Eiver 

 with its branches drains the larger part of 

 the district. ISToncut Creek on the north 

 and Bear Eiver on the south are the only 

 other streams of importance. 



Geology. — Sedimentary formations occupy 

 comparatively few areas in the district, all 

 of which have been tentatively referred to 

 the Calaveras formation, no fossils having 

 been found in them. They consist of slates 

 and quartzitic sandstones, usually with 

 northerly strike and steep easterly dip. 

 Diabase and porphyrite occupy large areas 

 in the central and southern parts, as well 

 as intrusive masses of granodiorite and 

 gabbrodiorite. Amphibolites, resulting 

 from the dynamo-metamorphism of diabase, 

 gabbro and diorite, also occur in several 

 places. The rocks of the district are prin- 

 cipally massive, in contrast to those of the 

 districts adjoining on the south and east. 

 However, two lines traverse it along which 

 extensive metamorphism has taken place 

 and schistose rocks have been developed. 

 The superjacent rocks, resting unconforma- 

 bly on the older series, consist of I^eocene 

 river gravels, together with beds of andesitic 

 and rhyolitic tuffs. Comparatively small 

 areas of these remain, the larger part hav- 

 ing been carried away by erosion. Pleisto- 

 cene shore gravels and alluvium occupy the 

 southwestern corner. The lone formation 

 is not well exposed in this district, being in 

 part covered by Pleistocene deposits, in 

 part removed by erosion. 



Economic Geology. — Important and rich 

 Neocene gravel deposits in this district have 

 been worked at Camptonville, Nevada City, 



North San Juan, Badger Hill, French Cor- 

 ral and Smartsville. Gold-quartz veins 

 occur scattered throughout the area, but by 

 far most of them are found in the immedi- 

 ate vicinity of Nevada City and Grass Val- 

 ley. These districts are among the most 

 important of the gold-mining regions in 

 California. Many of the rocks of the dis- 

 trict are adapted for building purposes. 

 The only one in extensive use is the grano- 

 diorite, near Nevada City. The often deep- 

 red soils in the foothill region are of resid- 

 uary origin. Extensive areas of alluvial 

 and sedimentary soils are found only in the 

 southwestern corner. 



INTERNATIONAL CLOUD OBSERVATIONS. 

 In a series of papers on the storm tracks 

 and allied phenomena, prepared under the 

 direction of the Chief of the Weather Bu- 

 reau, much has been written about the 

 cyclonic circulation at the surface of the 

 ground, but the subject would be very in- 

 complete without alluding to the eiibrts 

 that are being made to determine the circu- 

 lations of the upper atmosphere all over the 

 globe. Theoretical solutions, to some ex- 

 tent confirmed by observations, have been 

 given, and yet the true connection between 

 the general and the cyclonic circulation has 

 not been properly cleared up and tested by 

 experience. So far as the general move- 

 ments are concerned, the components are 

 somewhat as follows in the northern hemis- 

 phere, those south of the equator being 

 counterparts. Along the meridian from 

 Lat. 24° to the equator the component is 

 south, t6 the pole it is north ; in middle 

 latitude, where the extra tropical cyclones 

 prevail, there is a northern component in the 

 middle cloud strata, and two southern com- 

 ponents, one near the ground and one in 

 the cirrus strata. Along the parallels of 

 latitude there are two systems of compo- 

 nents; from 0° to 35° latitude, a westerly 

 component at the surface, and an easterly 



