2 PROCEEDINGS OF THE GEOLOGICAL, SOCIETY. [NoV. 17, 



St. Mary's ; 0° 32' East of the point of observation at St. Michael's. 

 Communicated by Major Guerra, a highly intelHgent officer of the 

 Portuguese army, resident at St. Mary's, to his correspondent 

 here. 



Point of Observation. — The chief town of Villa do Porto, situated 

 on the south-west coast, about 200 feet above the level of the sea, 

 and separated from it by a slightly ascending plain, nearly three miles 

 wide, and W.S.W. (true) of the base of the central ridge, of which 

 the principal peak, Pico Alto*, is 1880 feet in height above the sea. 



Time and Phenomena. — At a little more than five minutes after 

 ten (10^ 8"^ at St. Michael's?), a slight subterraneous rumbling was 

 followed by a sufficiently perceptible oscillation from south to north, 

 ending in a strong shock, and lasting not less than three seconds. 



Effects. — No damage appears to have been done to houses and 

 public buildings. 



St. Michael's ; Point of Observation 25° 41' West of Greenwich. 



Point of Observation. — The chief town of Ponta Delgada, close to 

 the sea, at an elevation of 70 feet, on an ascent which in about three 

 miles reaches to the top of the central ridge of the island, which in 

 this part rises into peaks of between 1000 and 1600 feet above the 

 sea. 



Time and Phenomena. — A distinct but not loud rumbling was 

 heard by some persons for about three seconds, and after a percep- 

 tible interval, a slight oscillation was felt, rapidly increasing in force, 

 and slightly diminishing at its almost sudden termination. The time 

 was ascertained by the stopping of clocks (which faced to the westward) 

 to be three minutes after ten p.m., and the duration estimated by 

 four persons, watch in hand and independently of each other, at six 

 or seven seconds. The first oscillation, as felt by persons sitting, was 

 thought to be from N.N.W. to S.S.E. (true), and open inkstands 

 were found to have overflowed on their northern and southern sides. 



Effects. — The balustrades, pinnacles, and crosses of some church 

 towers were throvra down ; a few houses fell entirely, or their roofs 

 or gables fell in, or the walls were rendered unsafe ; of others the 

 chimneys and walls were cracked in sides and corners, or the ceilings 

 shaken, or the wrought stone eaves dislodged, and some windows 

 strained, but the glass not broken ; many garden walls were shaken 

 down or gapped at the top, or left in a falling condition, and high 

 roadside banks were thrown down. The damage so caused does not 

 appear to have been aflfected by aspect, situation, or strength of ma- 

 terials and construction. Gaps may be seen in the strongly built 

 corners of garden walls at one side of a road, where loosely built en- 

 closures were left uninjured at the other ; and a new farmhouse was 

 entirely thrown down at the west end of the island, surrounded by 



* See Mr. Hunt's paper on the Geology of the Island of St. Mary's, Quart. 

 Jouva. Geol. Soc. vol. ii. p. 39. 



