572 



NATURE 



{Oct. 13, 1887 



The History and Cause of the Subsidences at Northwich and 

 its Neighbourhood, in the Salt District of Cheshire, by Thos. 

 "Ward. — The frequent occurrence of subsidences in the neigh- 

 bourhood of Northwich makes it desirable to learn their history 

 and cause. Northwich overlies extensive beds of salt. These 

 occupy about three square miles. The first, or "top " rock-salt, 

 lies at a depth of about 50 yards from the surface, and is covered 

 by Keuper marls, and these by the drift-sands and marls. Be- 

 tween the two beds of salt there are 30 feet of indurated Keuper 

 marl. The second, or " bottom " rock-salt, is over 30 yards in 

 thickness. The subsidences which are so destructive in the 

 town of Northwich and the neighbourhood are entirely caused 

 by the pumping of brine for the manufacture of white salt. It 

 was only about 1770, or shortly afterwards, that the first sinking 

 was noticed ; since that date, subsidence has gone on very 

 rapidly, and much destruction of property has resulted. Large 

 lakes or " flashes," one of more than 100 acres in area, and of 

 all depths up to 45 feet, have been and are being formed. This 

 peculiar phenomenon of subsidence in the salt-districts is worthy 

 of more consideration than it has hitherto received from scien- 

 tific men. 



The Sonora Earthquake of May 3, 1887, by Dr. T. Sterry Hunt, 

 F.R.S., and James Douglas. — On the afternoon of May 3, 1887, 

 at 2.12 Pacific time (= 120° W. of Greenwich), the first of a 

 series of earthquake movements was felt in the State of Sonora 

 and the adjacent parts of Mexico and the United States, over 

 an area extending from El Paso in Texas on the east to the 

 River Colorado and the Gulf of California on the west, and from 

 the State of Sinoloa on the south as far north as Albuquerque in 

 New Mexico ; the extremes in both directions being over 500 

 miles. It was the fortune of the writers to be at the time at the 

 great copper-mining camp of Bisbee in Arizona, in a narrow 

 gorge of the Mule Pass Mountains, about 5300 feet above the 

 sea, and near the border of Sonora. A violent tremor of the 

 earth, including two sharp shocks, and lasting over ninety 

 seconds, was succeeded at frequent intervals by many minor 

 movements in the next three days, and, less frequently, at least 

 up to May 29. In this part of Arizona solid house-walls, of 

 adobe or unburned brick, were cracked or overturned, while 

 huge rocks in the steep mountain gorges rolled down, causing 

 much damage. Fires, perhaps kindled by these in their course, 

 appeared immediately afterwards in various wooded regions in 

 Sonora and Arizona, giving rise to many false rumours of 

 volcanic eruptions. The movement here seemed from south to 

 north. The small town of Bavispe in the Sierra Madre in 

 Sonora was nearly destroyed, many people being wounded and 

 forty-two killed. Opoto suffered in a similar way, and Fronteras 

 to a less extent. The district chiefly affected by the earthquake 

 is, however, for the most part a desert, with some cattle ranches 

 and mining stations. Interesting studies were made by the 

 authors in the valleys, or mesas, between the parallel mountain 

 ridges in this region, both in the San Pedro and Sulphur Spring 

 Valleys. The latter, to the east of Bisbee, and stretching north 

 and south about loo miles, is often 8 or 10 miles wide, and 

 has its lower portion in Sonora. Though without a visible 

 watercourse, water is there generally found at depths of from 

 10 to 40 feet in the numerous wells sunk at intervals to supply 

 the needs of large herds of cattle. As described by many 

 observers, the surface of this plain was visibly agitated by the 

 first . earthquake shock, so that persons were in some places 

 thrown down by the heaving of the soil, which burst open with 

 discharges of water, while the wells overflowed and were 

 partially filled with sand. In the southern part of this valley, 

 for about 7 miles south from the Mexican frontier, the 

 authors found the results of the undulatory movement of the soil 

 apparent in great numbers of cracks and dislocations. For 

 distances of several hundred feet, along some lines with a gener- 

 ally north and south course, vertical downthrows on one side of 

 from I foot to 2 feet and more were seen, the depressed portion 

 rising either gradually or by a vertical step to the original level. 

 Branching, and in some cases intersecting, cracks were ob- 

 served. These depressions were evidently connected with out- 

 bursts of sand and water, which, along cracks, marked by 

 depressions on both sides, sometimes covered areas of many 

 hundred square feet with layers a foot or more in depth, marked 

 here and there by craters 2 feet or more in diameter, through 

 which water had risen during the outburst of these mud vol- 

 canoes. While the earthquake movements in the adjacent hills 

 of Paleozoic strata had left no marks, the dislocations over 

 many square miles in the valley would have sufficed to throw 



down buildings and to cause great loss of life in an inhabited 

 region. There are believed to be no evidences of previous 

 earthquake disturbances in this region since its discovery by the 

 Spaniards centuries ago. From the published reports of commis- 

 sioners named by the State of Sonora, it appears that the 

 regions injured by the earthquake are in two nearly parallel 

 north and south valleys in the district of Moctezuma, along the 

 River Bavispe, a tributary of the Yaqui. In both regions are 

 noticed the opening, in the arable lands, of numerous fissures, 

 generally north or north-east in direction, from many of which 

 water flowed abundantly. The river thus supplied in a time of 

 excessive drought swelled to the volume usual in the rainy 

 season of summer, a condition which lasted up to the time of 

 the report of Senor Liborio Vasquez, dated at Bavispe, May 29, 

 1887. The fields had become green and the air nnist with pre- 

 vailing fogs. A report concerning the region of Opoto mentions 

 not less than seven volcanoes in the vicinity, which were seen 

 burning for two days, but without any flow of lava ; while that 

 for the Bavispe region declares that no volcano had there been 

 discovered. The authors incline to the belief that, as was the 

 case in the San Jose Mountains, and others examined by them 

 along the borders of Arizona, the appearances of volcanoes near 

 Opoto were due to forest fires. 



The Disaster at Zug on July I, 1887, by the Rev. E. Hill.— 

 On July 5, 1887, at the town of Zug, in Switzerland, a portion 

 of the shore gave way and sank into the lake. About three 

 hours later another much larger adjacent area also suddenly 

 subsided, so that in all an area considerably over two acres, 

 with half of one of the principal streets, was submerged to a 

 depth of about 20 feet. It can be seen that the subsoil consists 

 of coarse gravel and sand, followed after a few feet by soft wet 

 sand and fine mud. According to Prof Heim, this fine mud or 

 sludge reaches to a depth of nearly 200 feet, and the disaster is 

 shown to be due to a flowing out into the lake of this mobile 

 sludge from under the superincumbent weight of buildings and 

 firmer ground. The buildings collapsed as they sank. The 

 catastrophe must have been long impending ; the exact cause 

 which precipitated it is indeterminate, but a low level of the 

 lake and tremors from pile-driving for new quays are suggested 

 as contributories. On the English coast the incessant changfes 

 of pressure from tides probably render impossible such instability 

 of equilibrium. 



The Triassic Rocks of West Somerset, by W. A. E. Us.sher. — 

 This paper is the result of investigations made in the years 1878 

 and 1879. The constitution, extent, and general relations of the 

 Lower, Middle, and Upper Triassic rocks of the area are briefly 

 described, with the following general results : — The Lower Trias 

 consists of breccia and breccio-conglomerate upon sands and 

 brecciated sand and loam ; it is faulted against Keuper basement 

 beds, and is conformably overlapped by Middle Trias marls upon 

 the margin of the older rocks. The Middle Trias consists of 

 marls with sandstones in places at their base ; it is faulted against 

 the successive divisions of the Keuper on the east, and terminates 

 northward in the angle made by converging faults at Bick- 

 noller. The Middle Trias marls rest on the older rocks near 

 Vellow W lod Farm, and finally disappear near Orchard Wynd- 

 ham, south of Williton, under Keuper breccias. The Keuper 

 beds consist of marls, sandstones, and a locally varying series 

 of conglomerates, gravels, and breccia in descending sequence. 

 The sandstones are very calcareous south of Crowcombe ; they 

 form marginal deposits in places near Dunster. The coarser 

 beds of the Keuper develop at the expense of the sandstones in 

 the area west of Williton. It is very probable that the Keuper 

 basement beds of the Porlock valley may be marginal deposits 

 formed during a progressive subsidence, and therefore may belong 

 to a higher horizon than the Lower Keuper beds south of 

 Williton. 



The Devonian Rocks of West Somerset on the Borders of the 

 Trias, by W. A. E. Ussher. — The composition of the Quantocks 

 is first briefly described, and the faulted relations of Middle Devo^ 

 nian grits, slates, and limestones of which they consist alluded 

 lo. From the constitution of the Palaeozoic districts on the east 

 and west of the Triassic rocks of Crowcombe and Stogumber, 

 the author considered the beds eroded in the intervening valley 

 would amply account f )r the variability of the Triassic strata de- 

 rived from them. Fro-n Withycombe to Porlock the faulted 

 relations of the Middle and Lower Devonian grits are then briefly 

 described. The author considered that the elevation of the 

 Quantocks, the Brendon, and the Dunkery ranges was \ 



