Figure A-18. Photographs of core samples from Trenton and Black River formations in Humble Riley No. 2, 26-3S-4W.

1. 4071 ft--Bryozoan packstone (Trenton). Combined moldic and fracture porosity is nearly 15% in this interval.

2. 4078 ft--Burrow-mottled wackestone, with abundant bryozoans and brachiopods (Trenton). Moldic and intercrystalline porosity is good in the packstone layers (top and bottom).

3. 4082 ft--Wackestone with burrows and abundant crinoidal grains (Trenton).

4. 4084 ft--Skeletal wackestone with cavernous porosity typical of porous intervals in the Albion-Scipio Field (Trenton). Both replacive dolomite and dolomite cements are moderately to highly ferroan.

5. 4167 ft--Wackestone with burrow-mottles and irregular contacts between thin packstone layer and surrounding wackestone (Trenton).

6. 4172 ft--Skeletal pack/grainstone (Trenton). Large, micritic intraclasts and good (10%) intercrystalline and moldic porosity.

7. 4180 ft--Shaly, skeletal wacke/packstone, which is completely dolomitized (Trenton). Moderate intercrystalline porosity.

8. 4185 ft--Large tan chert nodule in wackestone (Trenton).

9. 4222 ft--Cherty lime wackstone, with mottled color (Black River). Dark skeletal fragments are phosphatic brachiopods.

10. 4224 ft--Cherty lime wackestone. Interval is 30% dolomite (Black River). Small veins are filled with (1) ferroan dolomite and (2) calcite.

11. 4227 ft--Dolomitic, cherty wackestone, showing undulose bedding (Black River). Small veins in top chert nodule are filled with dolomite cement.

12. 4228 ft--Slightly dolomitic bryozoan wackestone (Black River).