1870.] HUNT — ON LAURENTIAN ROCKS. 7 



of the blood in the membrane between his toes. At first he 

 disliked thus being bandaged up like a mummy ; but frogs, like 

 ourselves, can accommodate themselves to circumstances. He 

 has figured before the public, under the microscope, during two 

 winters, but has since died. 



We shall now glance at a creature of a difi*erent order and 

 class — a crustacean — the American Cray-fish (^Astacus Bai'tonii)^ 

 and a curious creature he is ; almost every thing suits his palate. 

 He is very provident, and lays up what he is unable to eat in the 

 holes under the .rock-work. He is a good gymnast, and can stand 

 on his head, or on his tail, or can walk as it suits him, — as fast 

 the one way as the other, — backwards, forwards, or sideways, — 

 it matters not. He hid himself for a time, as his coat was getting 

 shabby and too small for him. He came forth at last with a 

 complete new suit; roamed about for some time, but has again 

 vanished, with no ostensible reason. This is the first instance of 

 this creature changing his shell in our aquarium. 



With the exception of a few species of water beetles, dytiscus, 

 aciUus, and coli/mhetes, which the fish gradually mastered — not- 

 withstanding the hardness of their elytra, — the curtain falls on 

 the denizens of our aquarium. 



We intend, in continuation of our aquaria studies, to lift the 

 curtain once more, and, with the assistance of the microscope, to 

 illustrate some forms of animal and vegetable life which cannot 

 be well seen by the unassisted eye. 



ON LAURENTIAN ROCKS IN EASTERN MASSA- 

 CHUSETTS. 



By Dr. T. Sterry Hunt, F.R.S.* 



In a paper read before the American Association for the 

 Advancement of Science at Washington in April, 1854, and 

 published in this Journal for September in the same year, (vol, 

 xvii, page 193,) I noticed the crystalline limestones of north- 



* From Silliman'sJournaUor January, 1870. 



