THIRD REPORT OF THE DIRECTOR I906 29 



The secondary twinning parallel to a hypothetic plane — Yi R 

 which was previously noted in connection with the calcite from 

 Crown Point, is developed tO' a marked degree in these crystals 

 where it takes the form of parallel systems of sharp ridges pro- 

 truding from the surfaces of the planes of both R and OP. On one 

 crystal, the basal plane of which measures 15.6 cm on the bounding 

 edges, one of these projections measures 4 cm in length and .5 cm 

 in hight. 



EARTHQUAKE RECORDS 



The seismograph installed in the basement of Geological Hall 

 was placed in operation on March 10, 1906. It has furnished 

 since that time a number of records which fully demonstrate its 

 mechanical efficiency and its utility as an adjunct to the Museum's 

 scientific equipment. Similar instruments have been in use for 

 some time in Baltimore, Washington and Cheltenham, Md., but with 

 these exceptions there are no other stations throughout the entire 

 eastern section of the country where the investigation of seismic 

 phenomena is proceeding at the present time. The records have 

 an independent value as a measure of the character of earth tremors 

 experienced in the region, while at the same time it is hoped they 

 will contribute to the general advance of this line of work which 

 is now receiving attention and support in many parts of the world. 



The disturbances thus far registered at Albany have originated 

 at remote points, none of them nearer than 2500 miles. In some 

 cases, however, the wave motions traced by the instrument have 

 been marked in their intensity, showing that local conditions are 

 not unfavorable to their transmission. The fact that no earth- 

 quakes could be traced to near-by sources can not be regarded as 

 indicative that the region lies without the bounds where sensible 

 movements originate, for observations must be extended over a 

 much longer period of time before any conclusions are warranted 

 as to the occurrence and relative frequency of local readjustments 

 such as give rise to earth tremors. 



In explanation of the accompanying data relating to the seismo- 

 graph records, it may be stated that the instrument used belongs to 

 the horizontal pendulum type. It is an invention of Omori. the 

 distinguished professor of seismology at the University of Tokio, 

 and has been later improved by the makers, Messrs J. & A. Bosch, 

 Strassburg, Germany. The instrument is placed on a concrete 

 pier set into the ground to a depth of 3 feet and resting upon 



