Topographical Features of the X^ew Haven region. Ill 



layer, although sometimes described as mud, is i)robably wet uncom- 

 pacted sand or gravel. 



4. That the hard-pan inay be in most cases the saiiie particular 

 layer of the drift formation ; but that we do not know facts enough 

 to authorize the assertion that this is true ; or enough to estal)lish 

 satisfactorily its probability. 



5. That the hard-pan in some cases is probably a gravelly layer 

 firmly compacted. The region north of the head of the harbor, in 

 the direction of the Canal railroad and the Mill River valley, is un- 

 derlaid, as has been shown (p. 71) by a very coarse gravel, as the re- 

 sult of the central tidal flow of the bay in connection with the cur- 

 rents of the streams ; and it is probable that this gravel-course ex- 

 tends out beneath the harbor; and this may be the hard-pan layer 

 that is reached by the piles. It would naturally have an inclination 

 seaward, following the slope of the bottom of the bay. Along the 

 valley of West River and that of the Quinnipiac, there were doubt- 

 less similar gravelly layers formed below, through like means, which 

 may be the hard-pan encountered in the beds of these streams. Yet 

 this is only a suggestion, to be tested by future examination. None 

 of the hard-pan has ever been brought up to the surface, and nothing 

 positive is known as to its nature or the cause of its hardness. It may 

 owe its hard-pan quality to a partial cementing of the material by 

 means of oxyd of iron, an ingredient always present in the sand and 

 gravel and the source of the prevailing color, and often causing the 

 waters that flow through them to become strongly chalybeate ; be- 

 sides being a common cement among rock strata. But the coarse grav- 

 el beneath State street and the Mill River region is in almost all parts 

 very hard digging, owing to its firmness, and for thick beds perhaps 

 nothing more in the way of firmness would be required than what 

 here exists. 



6. That the hard-pan layer is usually sufficiently water-tight, or 

 close in texture, to carry fresh-water along it from the land, following 

 its seaward slope, and thence to become a source of fresh-water for 

 artesian wells in the harbor. The flow of fresh water in a layer be- 

 neath the bay is evidence that this layer probably continues inland, 

 and is a seaward part of a sloping water-bearing layer beneath the 

 plain. The fact that the wells of the central and lower part of the 

 New Haven plain generally descend into a gravelly layer is favorable 

 to the view that the hard-pan is gravelly. Yet a layer of clayey sand 

 is equally retentive of water, and will as well hold up the fresh-waters 

 flowing seaward from the land ; and when the wells of the plain as 



