LABRADOR CONCRETIONS 



615 



the south l)aiik of the Hamilton Eiver are composed chiefly of argilla- 

 ceous calcium carbonate. A thin shell of limonite surrounds this interior 

 portion of the concretion. Many of these concretions consist of hard, 

 well-indurated material encased in a thin shell, sometimes a sixteenth of 

 an inch or more in thickness, consisting of a very soft material easily 

 indented by a knife point or the thumb nail. Some of the Kenemich 

 Eiver localities also furnish t^q^es of concretions not seen elsewhere. At 

 one of these all of the concretions consist of sand cemented by iron which 

 has accumulated along the sides of small roots. The roots are sometimes 

 visible in the sections of these pipelike concretions of sand and iron, and 

 when broken into sections the central opening left by the root gives them 

 the appearance of large disk-shaped beads. 



The Lake Melville concretions show every possible relationship to the 

 fossil Pleistocene shells from that with the shell occupying the position 

 of a tyi^ical centrally placed nucleus, as in figures 1 and 2, plate G, to 

 examples in which the shell is entirely on the surface of the concretion, 

 as in figure 3, plate 6. Other specimens show opposite ends of shells 

 like Mytilus extending out on either side of an irregular-shaped concre- 

 tion which has completely enveloped the middle portion of the shell 

 (plate 6, figure -i). Many examples occur in which the concretion is 

 attached to a small portion of a granite pebble (plate 5, figures 2 and 3 ) , 

 while others have numerous pieces of fine gravel projecting from their 

 sides. The numerous rings which mark the surface of many of the sub- 

 spherical concretions at right angles to the shorter axis represent the 

 lamination of the beds in which they occur. Such concretions when 

 ground show the lamination planes continuing through the concretion 

 in line with the encircling rings on the surface (plate 6, figures 7 and 9). 

 The specimen when ground will often split along the lamination plane, 

 thus showing the weakness and imperfect cohesion characterizing these 

 lines. Some of the marine clay on the shore of Lake Melville is without 

 any trace of lamination. The section 6 miles west of Long Point exposes 

 4 feet of clay without lamination in which subspherical concretions occur. 

 The fine lamination of some of these clays, however, is indicated by the 

 fine elevated lines on such specimens as figures 7 and 9, plate 6. 



A noteworthy feature of the Labrador concretions is the large per- 

 centage of specimens with an organic nucleus. Concretions with a visible 

 nucleus of any kind are said to be rare in the Pleistocene clays of the 

 Connecticut Valley. Professor Hitchcock states that "In no case in 

 Massachusetts have I seen an organic relic as a nucleus." -'* In speaking 



-» Edward Hitchcock : Final report on tlu- geology of Massachusetts. 1-S41. pp. 406-418. 



