PHYSICAL HISTORY OF NEW HAMPSHIRE. 543 



Subsequently to the cold term indicated by the boreal marine shells, 

 there are two classes of facts serving to indicate since that time, and 

 probably within the human period, a long era when the climate over 

 New Hampshire was milder than it is now. The evidences derived from 

 our limits are the scanty remains of southern plants procured in a very 

 few localities. They may be well represented by the Rhododendron max- 

 imum, mentioned in the catalogue of plants as occurring in Richmond, 

 Fitzwilliam, and Grantham. Since the printing of that chapter, I have 

 got traces of it in Hopkinton and Hooksett. The proper home of this 

 shrub is in the Middle states. Its occurrence in insulated swamps sug- 

 gests a former abundance in intermediate localities, and the presumption 

 of a climate more like that of Pennsylvania, to enable it to flourish 

 within our borders. 



The other class of facts is represented by the discovery of several 

 kinds of marine animals that properly flourish south of Cape Cod, on 

 the coast of Maine, and the British provinces. The nearest locality is at 

 Quahog bay, about thirty miles beyond Portland. More than twenty 

 species of marine animals, according to Prof. Verrill, live in this bay, the 

 most common of which is the quahog or round clam, whose proper hab- 

 itat lies to the south of Massachusetts bay. Scarcely any of them are 

 known to occur off the New Hampshire coast. In their stead are the 

 more northern species, such as are at home in the waters of the Can- 

 adian district. This assemblage of extra-limital species is called a 

 "colony," and, in order to understand why they live in such a place, iso- 

 lated from their kindred, we may use the same theory which has just 

 been applied to the occurrence of the Rhododendron* The climate for- 

 merly allowed the Alleghanian animals, as well as plants, to abound 

 where now the colder Canadian species find the conditions of life con- 

 genial, and suitable for productiveness. 



Another of these southern forms is the oyster. This occurs, living 

 naturally, in the Sheepscot and Harriseeket rivers in Maine. It is sup- 

 posed that both these edible mollusks once flourished along the whole 

 coast. Further evidence is afforded by the discovery of numerous heaps 

 of their shells in the piles of rubbish left by the aborigines, who used 

 the animals for food. These heaps occur very commonly along the 

 whole New England coast; and they seem to indicate that this milder 



