1882.] 85 [Hinckley. 



folding of the rocks must observe the same law in their distribu- 

 tion in depth. For it is reasonable to suppose that crust-strains 

 originating in the shrinking of the earth's interior will culminate 

 in the more superficial portions of the crust. 



Hence, in conclusion, we may safely say that every theory of 

 the origin of joint-structure now entertained by geologists (and 

 in a certain sense they are all true, some explaining one kind of 

 jointing and some another) is consistent with the view that joint- 

 ing is essentially a superficial feature of the earth's crust. 



NOTES ON THE DEVELOPMENT OF RANA SYLVATICA 



LECONTE. 



BY MAEY H. HINCKLEY. 



Of the species of Rana found in Milton, Massachusetts, R. syl- 

 vatica congregates at the water earliest in spring, for purposes of 

 egg-laying. The time of appearance varies with the season, ac- 

 cording as the mild weather is early or late. In 1880 they were 

 seen Feb. 28, while in 1881 and 1882 they were not found till 

 March 18, and 23. Their appearance in these years was preceded 

 by three or more days in which the temperature of the air at 

 mid-day ranged from 40° to 60°. The frogs apparently collect 

 immediately on awakening from their torpor, in the shallow 

 water, on the sunny side of small ponds, inundated swamps, and 

 bogs. On sunny days the still shallow water near the shore will 

 be found several degrees warmer than that which is deeper or in 

 shadow. My notes give the lowest temperature of water in 

 which I have seen the frogs moving, 45° ; the lowest in which 

 they were found spawning, 50 . 1 After collecting at the water 

 they are evidently only affected by the temperature of the air 

 indirectly as it affects the water. I have heard R. sylvatica in full 

 voice in the evening when the air was 30°, but this occurred after 

 a mild sunny day, and probably before the water had become 

 chilled by the night air. In water at a temperature of 45° the 

 frog lacks its usual agility and floats about like a dead leaf on the 



1 See notes on the Toads and Frogs about Cambridge, Mass., by Mr. F. W. Putnam, 

 in these Proceedings, Vol. ix, p. 229. Also notes on Batrachians found in the vicinity 

 of Springfield, Mass., by Mr. J. A. Allen, these Proceedings, Vol. xn, p. 196. 



