TRANSACTIONS OF SECTION C. 713 



vertical step to the original level. Branching, and in some cases intersecting, 

 cracks were observed. These depressions were evidently connected with outbursts 

 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 two feet or more in diameter, through 

 which water had risen during the outburst of these nnid volcanoes. The authors 

 examined many of these phenomena in northern Sonora, and took photographs, 

 which were exhibited. They note that while tlie earthquake movements in the 

 adjacent hills of Palseozoic 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 commissioners named by the State of Sonora it 

 appears that the regions chiefly 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. The town of Bavispe itself, of 1,500 souls, lies about seventy 

 miles south of the American frontier and 110 miles south-east of Bisbee, Arizona ; 

 its elevation being 3,070 feet above the sea. Here forty-two persons were killed 

 and twenty-five wounded. Bacerao, twenty miles farther south, also suflered 

 much damage, and the estimate for property destroyed in this valley was 218,190 

 dollars. Opoto, Guasalas, Granados, Bacudebachio, and Nacovi lie in a lower 

 valley about thirty miles west of the last, the elevation of Guasalas being only 

 1,720 feet above the sea. The loss of life was here confined to (>[5oto, where nine 

 were killed and six wounded. The injury done to property in this valley was 

 estimated at 78,115 dollai-s. 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 Seuor Liborio Vasquez, dated at 

 Bavispe, May 29, 1887. The fields had become green and the air moist with prevail- 

 ing 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. 



6. TJie History and Cause of the Siihsidences at Nortlnvich and its Neigh- 

 bourhood, in the Salt District of Cheshire. By Thomas Ward. 



The frequent occurrence of subsidences in the neighbourhood 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 fifty yards from the 

 surface, and is covered by Keuper marls, and these by the drift sands and marls. 

 Between 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. These beds of salt 

 occupy the lowest portion of an old Triassic salt lake. 



The first bed of rock-salt was discovered in 1670, the second in 1781. From 

 about 1730, at which date the river Weaver and the M'itton brook were rendered 

 navigable, until after 1781 all the rock-salt mines were in the ' top ' bed, and the 

 whole of these, with one exception, have been destroyed, and in almost every case 

 by water, leaving funnel-shaped, nearly circular, holes. These are now filled with 

 water and are known as ' rock pit ' holes. The rock-salt mines are now in the 

 lower bed and very rarely fall in. When worked to the boundary, water and 

 brine, either or both, break in or are let in, and the mines are utilised as huge 

 reservoirs. 



The falling in of a rock-salt mine is now a very rare occurrence, and subsidences 



