OF ARTS AND SCIENCES. 



101 



and South America, and suggest the mode of formation of the great 

 deserts. Ascending to the earlier periods of geology, it will account 

 for the situs of the aqueous deposits in those periods, as the post-plio- 

 cene, tertiary, and cretaceous. The views presented in the memoir 

 are the result of a study of the tidal currents on the alluvial shores of 

 the United States, and particularly on the New England coast. This 

 study has led to the discovery of a threefold relation in form, amount, 

 and locality between these currents, and the materials transported by 

 them. The certain relation between the tidal currents and the allu- 

 vial deposits in structure, position, and amount establishes a principle 

 of conformation in the latter, by means of which the geologist will be 

 enabled to reason back from the deposits of earlier periods to the na- 

 ture of the currents by which they were made, as the character of the 

 present formations on the borders of the sea and in its depths is readily 

 decided when the peculiarities of the local currents are ascertained." 

 [This memoir has been printed in extenso in the current volume of the 

 Memoirs of the Academy, Vol. IV., New Series.] 



Dr. Pierson read a communication from Dr. Usher Parsons, 

 of Providence, giving a detailed account of a tornado that 

 passed near Providence, Rhode Island, at 3 o'clock, P. M., 

 taken from minutes made at the time. 



" Whilst a heavy rain was falling, a black cloud was seen in the 

 west, which seemed to send down towards the earth a very dark elon- 

 gated cone. It commenced its career, as its traces afterwards proved, 

 in Johnston, about five miles west-southwest of Providence, and moved 

 in a north-northeast direction, at the rate of ten or twelve miles the 

 hour, passed across the head of Narraganset Bay, and moved onward in 

 a straight line eight or ten miles, towards Dighton. The blackest part 

 of the cloud was the centre of its under or convex side, whence the 

 cone descended. There soon appeared floating substances, both in the 

 cone and cloud, which were mistaken by many persons for birds whirl- 

 ing about and carried along seemingly unable to extricate themselves 

 from the vortex. Among its first ravages was an orchard in Johnston, 

 the trees of which were uprooted or broken, and the fences, and even 

 stone walls, were swept away. Passing along over the summit of a hill 

 or ledge of rocks one hundred feet high, it overthrew and demolished a 

 small powder-house, containing thirty kegs of powder used in blasting, 

 and neither the kegs nor their contents have ever been found. Near 



