ACADEMY OF NATURAL SCIENCES. 153 



In United States, east coast. 1850, three shocks ; 1851, seven shocks ; 1852, 

 ten shocks ; 1853, thirteen shocks ; 1854, eleven shocks. Total, forty-four 

 shocks. 



Balance against east coast, seven shocks. 



West India Islands. 1852, seven shocks : 1853, three shocks ; 1854, one 

 shock. Total, eleven shocks. 



These inclusive with the continental series foot up eighteen days on which 

 shocks occurred in excess of this coast during the same period of time, and 

 thus shows a margin of greater frequency of little more than thirty per cent. 



ERRATUM. 



Page 131, line 16 from bottom, for " an oven" read " or even." 



Regular Meeting, May 2d, 1864. 



Dr. Trask in the Chair. 



Eleven members present. 



Donations to the Cabinet : Specimens of dried plants, the types 

 of species lately described in these proceedings by Prof. Gray. 

 Mr. Brewer presented for Mr. Gabb the following paper : 



On Cretaceous Fossils from Sahuaripa Valley, State of Sonora, 

 Mexico, discovered by August Remond 



BY W. M. GABB. 



Mr. Remond announced in a letter to me, the discovery of fossiliferous rocks 

 about a league and a half east of Arivechi, Sahuaripa Valley, Sonora, Mexico. 

 The fossils occur in a clay slate, and are in a fine state of preservation. He 

 says : " The shales rest on sandstones, barren of fossils ; feldspathic porphyries 

 protrude through them, but no alteration of the beds were observed at the points 

 of contact. Even the lamination of the fossiliferous strata has not been dis- 

 turbed, and shells are found but a few millimetres from the porphyry." He adds 

 that the fossil bearing strata may attain a thickness of four or five hundred feet. 

 The shales are overlaid by thick strata of compact blueish limestone. The 

 strata dip to the south-east with an inclination of from thirty to fifty degrees, 

 and form the first range of foot-hills of the Sierra Madre. 



I have identified the following species on a hasty examination, proving con- 

 clusively the cretaceous age of the formation. It is an interesting fact, that 

 the fossils indicate a closer relationship to the eastern deposits than to those of 

 California. 



