1B0 SHIMER AND GRABAU HAMILTON GROUP OF THEDFORD 



that the characteristic species of each of the three divisions are restricted 

 to it. He makes the middle or coral zone thicker than it really is, for 

 the total thickness of this division, inclusive of the Encrinal limestone, 

 is only a little over 5 feet in both localities where its entire thickness is 

 shown. The characteristic corals appear to be entirely confined to these 

 beds, occurring chiefly in the shales above the Encrinal limestone. They 

 are often found on the talus slopes below this level, but we did not 

 observe them above this horizon, where their place is taken by the Alcy- 

 onarian corals. Logan * mentions an exposure " on the twenty-fifth lot 

 of the fifth range of Bosanquet," which furnished the characteristic fossils 

 of the coral layer and which he considered as probably above those found 

 in the third range, where he finds about 100 feet of shales overlying the 

 Encrinal limestone. This latter section is probably the one found in 

 Rock glen, though our measurements show less than 50 feet of shales 

 and calcareous beds above the. Encrinal limestone. It is safe to say that 

 the outcrop of , the coral zone mentioned by Logan as occurring on the 

 twenty-fifth lot of the fifth range (which we believe to be the same as that 

 described under Section B, though we have no map to verify this) is not 

 above the Rock Glen beds, but is equivalent to the Encrinal limestone 

 and the coral-bearing shales immediately above, both of which are near 

 the middle of the Rock Glen section. 



Our measurements at Rock glen give a trifle less than 38 feet of shales 

 above the Encrinal limestone, succeeded by about 9 feet of calcareous 

 beds. There may be other beds above these calcareous ones which 

 we have taken no account of, and thus the total thickness of the Upper 

 Hamilton beds exposed on the Riviere aux Sables and its tributaries may 

 be 102 feet, as given by Logan. 



In the Rock Glen section we found the coral layer (bed 3) 31 feet thick, 

 resting directly on the Encrinal limestone. At Bartlett's mills (bed 3) it 

 has the same thickness and position. At the Brickyard (Section C, bed 3) 

 only 2 feet are exposed, this being the highest bed shown here. The 

 thickness of the coral layer at Section B could not be ascertained, but it 

 holds the same relation to the Encrinal limestone as at the other local- 

 ities. It is not exposed at the railroad cut at Thedford (Section A), 

 where it probably occurs at a distance of about 15 feet below the level 

 of the railroad track. 



Twenty-six and a half feet above the coral layer at Rock glen, or nearly 

 30 feet above the Encrinal limestone, occurs a two-foot shale bed in which 

 Spirifer mucronatvs var. thedfordensis is most abundant (8a). The only 

 other exposure of this bed is in the railroad cut near the middle of Section 



* Page 3^5 of his 1863 report. 



