180 GLACIAL HISTORY. 



a portion of this subsoil of the city copied from a daguerreotype. 

 The large angular stones consisted of Alpine limestone, sernifite, 

 and Miocene ; one block of limestone was abont 10 feet long 

 and 4 feet high. The smaller, rounded and smoothed pebbles 

 are composed of the same materials ; they surround the large 

 blocks, and are intermixed without order. Numerous large 

 blocks lay in the ground near St. Anna and the Felsenhof ; some 

 also appeared in the mound of the Botanic Garden. At the 

 Sellnau, the construction of the road and the diggings for the 

 foundations of houses opened up the interior of the hill, which 

 consisted entirely of erratics *. The road-cutting executed in 

 1864 near the Brandschenke exposed a great quantity of Alpine 

 rocks, among which were vast blocks of sernifite and Alpine 

 limestone, confusedly mingled with large fragments of sandstone 

 and conglomerate. 



The fourth moraine of the basin of the Limmat may be traced 

 from the monastery of Fahr, through Schonenwerd to Alt- 

 stetten ; and the fifth is to be seen at Spreitenbach, Kilwagen, 

 and Oetweil. 



In the valley of the Glatt similar hills, forming a sort of 

 parapet, appear in the neighbourhood of Schwerzenbach, Ofen, 

 and Diibendorf, rising some 50 feet above the bottom of the 

 valley. 



The hills here referred to are in general covered with vegeta- 

 tion, and it is only by accident that their internal structure 

 becomes known. But in a great many places the blocks lie 

 separately on the surface of the ground, either isolated or piled 

 up into great heaps, and are called Erratic blocks or boulders. 

 Many of them are of extraordinary size, and have received 

 popular names. The plough-stone, which lies 140 metres (or 

 about 153 yards) above the sea-level between Erlenbach and 

 Wetzweil, stands out of the ground more than 60 feet ; and, 

 notwithstanding the diminution which it has already undergone, 

 it contains (according to Prof. Escher de la Linth) about 72,000 

 cubic feet of stone, and weighs about 90,000 hundredweight. 

 Another gigantic block stood near Hongg, and furnished the 



* In the spring of 1870, in digging for the foundation of a maypole here, 

 an enormous block was found; it has been placed in the Annex of the 

 Palace of Justice as an evidence of the ancient moraines. 



