217 



world's vegetable productions, and a critical study of our native 

 flora, which his own frequent discoveries have enriched. 



Resolved, That the proffer of this rare collection of plants is 

 gratefully and cordially accepted ; and the Corresponding Secre- 

 tary is instructed to inform Mr. Greene of this acceptance, trans- 

 mitting a copy of these resolutions. 



Mr. Sprague stated that the Herbarium is particu- 

 larly rich in specimens collected by various Exploring 

 Expeditions, both of this country and of Europe ; reports 

 of some of which have not as yet been published. Very 

 many of the plants are new to the Society's cabinet, and 

 the collection altogether is very extensive and exceed- 

 ingly valuable. 



Prof. Wm. B. Rogers made some remarks upon a 

 peculiar geological condition which he had noticed in 

 the Slate Rocks of Governor's Island, in Boston Harbor, 

 and of which he had never seen any notice. 



At the landing near the fort, where the slate is exposed, he 

 had observed a series of ledges of dark grayish-blue slate, in 

 which is exposed a species o? fault known as horizontal heave. 

 There are two lines of direction in the beds, and these are at 

 right angles with each other. This phenomenon of horizontal 

 heave, combined with the system of cross cleavage which is at 

 right angles with the planes of bedding, creates some obscurity 

 in some spots as to which are the original planes of bedding. In 

 other localities, and especially in the Quincy and Braintree 

 siliceous slate in which trilobites have been recently found, the 

 same difficulty exists ; rendering it impracticable to obtain perfect 

 specimens of that fossil in any amount, since the rock splits off 

 in an opposite direction to that in which the animal was de- 

 posited. 



This system of horizontal heave has been extensively studied 

 in Europe, and has elicited much discussion from geologists and 

 physicists upon the theory of the phenomena engaged in its pro- 

 duction. It is supposed that a great pressure has been applied 

 to the rocky mass, either before or after it had reached a com- 



