A DEEP SECTION IN OLD MARKET STREET. 77 



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BY W. W. STODDART, F.C.S., F.G.S. 



A GOOD section through the strata which underlie the centre 

 of the city can so seldom be actually seen, that every one that 

 occurs should be preserved. We are indebted to Mr. W. J. Rogers, 

 for that now brought before our notice, and it was obtained while 

 sinking a well in Old Market Street, in the hope of finding a 

 plentiful supply of water suitable for brewing purposes. 



The city of Bristol is built on the surface of a basin shaped valley, 

 formed by the coal measures, over which lie about 300 feet of 

 Keuper marls. These are again covered up by about 10 or 20 feet 

 of alluvium with one or two layers of sand and gravel. This valley 

 is sheltered from the cold north winds, by high hills of Millstone 

 Grit, which reach an altitude of 260 feet. 



The layers of sand and gravel are very pervious to water, and 

 consequently freely admit the percolation of the tide. The 

 surface of the alluvial ground is not more than 20 feet above the 

 mean sea level ; while some localities as at St. Philip's, Temple and 

 Canon's Marsh are so low that the free use of piles is necessary 

 for obtaining a firm foundation for buildings. It is this low 

 altitude, and the contorted form of the river that cause the un- 



