the Neighbourhood of Lisbon. 131 



the buildings destroyed, nearly as many were consumed by fire as overthrown by 

 the shocks. 



With the help of a very detailed account of each parish in Lisbon, published in 1 758 

 by Joao Baptista de Castro, in the fifth volume of his ' Mappa de Portugal', and after 

 a careful examination of the age of the principal buildings, I coloured a map of Lisbon 

 in such a manner as to show the violence of the earthquake in the different parts of 

 the town. No mischief whatever was done westward of a line which nearly corre- 

 sponds with the Rua de San Bento. J. B. deCastro's assertion of this fact is very deci- 

 sive, and there are two structures further west which would have been the first to 

 have fallen, had the shock been as violent in that district as in the centre of the town: 

 the great bridge of the aqueduct over the valley of Alcantara was not injured, a 

 prevalent tradition also says, that only one stone of the parapet was thrown down 

 by the earthquake ; and the beautiful gothic church of St. Jerome at Belem, with 

 its lofty stone roof supported upon very slender columns, remains uninjured. 



The principal force of the earthquake was confined to the valley reaching from 

 the public walk to the Terreiro do Paco and to the low streets which run along the 

 side of the river from the corn-market as far as Boa Vista ; the lower parts of the 

 adjoining hills also suffered considerably; but beyond these limits, the damage done 

 was not great : the quarter of Alfama, behind the castle, consists entirely of old 

 houses, and the northern suburbs suffered but little. 



I next inquired whether the district thus selected by the earthquake corresponded 

 with the distribution of the strata on which the city stands. It is never easy to 

 determine the exact boundaries of strata beneath a town ; still the irregular, unfi- 

 nished manner in which Lisbon is built, the unevenness of the ground, and a num- 

 ber of drains which were opened in diffierent parts of the town, enabled me to form 

 a tolerable geological survey. The west end of the city stands upon the Hippu- 

 rite limestone, and the rest upon the Almada beds, which are nearly horizontal, 

 and overlie the Hippurite limestone unconformably, so that the lower tertiary 

 beds are not brought up to the surface at the junction of the two formations; all 

 the higher parts of the town stand upon the upper Almada beds, and the lower 

 streets upon the blue clay, which has been left exposed by the denudation of the 

 upper beds. 



On comparing my two maps of the city, I found a very striking resemblance, 

 which I had not expected. The greatest force of the earthquake was confined to 

 the area of the blue clay, and not one of the buildings which stood upon that bed 

 escaped ; those upon the slopes of the hills standing upon the beds immediately 

 above the clay, suffered very severely, and the whole of the tertiary strata were 

 more or less affected by the shocks. On the contrary, all the buildings erected 

 upon the Hippurite limestone and the basalt escaped entirely ; the line at which 



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