Grabau — Faunas of the Hamilton Group. 



235 



the lower part of the Moscow shale. This shell has not otherwise been, 

 found in the Moscow shales of Eighteen-mile creek, but is abundant in the 

 limestone beneath. 



The Encrinal limestone has an average thickness of about one and one- 

 half feet, occurring usually as a single layer. AVhere weathered, it is seen to 

 be made up of comminuted organic remains, among which fragments and joints 

 of crinoid stems predominate. In places the upper part of the bed is some- 

 what shaly, and it is in this part of the rock that lamellibranchs are chiefly 

 found. The lower compact and semi crystalline portion of the rock contains 

 heads of Fa/oosites Hamiltonics and other corals. 



While this is the condition existing at Eighteen-mile creek, and on the 

 lake shore for some distance above and below the mouth of the creek, at 

 Morse creek, seven miles north-east, along the strike of the bed, the lower 

 portion of the limestone is of a shaly character. It is this portion of the rock 

 which contains the corals ; heads of Favosites Hamiltoiike two feet or more in 

 greatest diameter occurring with Heliophyllv/m Haiti and //. confluens. 



The specimens obtained from the Encrinal limestone seldom preserve their 

 surface features, owing to the readiness with Avhich they exfoliate. It is only 

 where Aveathering has removed the surrounding matrix, that perfect specimens 

 have been obtained. 



Forming, as it does, a dividing line between the Hamilton shales beneath, 

 and the Moscow shales above, and retaining its individuality throughout this 

 region, this limestone becomes a convenient reference stratum, from which the 

 subdivisions of the two shales can be measured, either upwards or downwards, 

 and in the following pages it is so used, all subdivisions being referred to it 

 as a datum plane. The bed is divided into blocks by two sets of joints, and 

 every year many of these become undermined and fall to the foot of the cliff, 

 where they often accumulate in great numbers. The lower face of the lime- 

 stone is usually coated with a thick layer of iron sulphide (probably 

 marcasite) from the oxidation of which the rock is usually much discolored. 



The Hamilton or Lower shales differ in lithologic character from the 

 Moscow shales mainly in their greater fineness, and probably a higher percent- 

 age of calcareous material. They are more fissile and their lamination is more 

 pronounced and regular. The indications are of deeper and purer water during 

 their deposition, and corresponding with these conditions, we have a greatei 

 abundance and variety of organisms Several courses of concretions occur, but 

 these are not as continuous as are those of the Moscow shales. The upper 

 four inches of shale immediately underlying the Encrinal limestone were 



