150 SHIMER AND GRABAU — HAMILTON GROUP OF THEDFORD 



which still awaits a comprehensive and detailed study. It was our good 

 fortune while at Thedford to make the acquaintance of Messrs Aldridge, 

 N. J. Kearney, and Charles Southworth, of Thedford, students of the 

 local geology. They generously conducted us to the most interesting 

 sections in the vicinity and aided us in making the collection on which 

 our study is based. 



Descriptions of the Sections 



in general 



We visited in all five sections in the Thedford region. These are : 



A. The cut about a quarter of a mile east of the Thedford station, on the Grand 

 Trunk railroad. 



B. An exposure on the hillside (old river bank) about three-quarters of a mile 

 north of the preceding locality. 



C. The banks of a small stream about a mile west of the preceding locality. The 

 clay of the lower beds is here dug for brick manufacture. 



D. Rock glen, about a mile east of Arkona, on a small tributary of the Riviere 

 aux Sables. 



E. Bartletts mills, now known as Marshalls mills, about a mile up the Sable 

 river from the mouth of Rock glen. 



In all of these exposures except the first a bed of limestone of nearly 

 constant thickness and uniform character is found. This bed, generally 

 called the Encrinal limestone, is readily recognized and serves as a datum 

 plane for the correlation of the beds above and below it. It marks the 

 dividing line between the upper and lower beds of the Hamilton group 

 of this region, a division which is based on abrupt faunal changes. 



SECTION A— THEDFORD 



This section is now largely overgrown, the banks being much weath- 

 ered, the shales changed to clays, and the calcareous beds shattered into 

 fragments, which cover the slopes. The fossils are weathered out, and 

 may be picked up in large quantities from the sloping bank. The most 

 abundant form is Spirifer mucronatus var. thedfordensis. This section is 

 between 30 and 40 feet deep, and may be divided as follows in descend- 

 ing order : 



9. Argillaceous thin-bedded limestones and calcareous shales, the former 

 containing chiefly fragments of brachiopods, as well as complete shells 

 and numerous branches of Ceratopora intermedia (Nicholson) and 

 Streblotrypa hamiltonense , 10 feet 



The following is a list of species obtained from these beds : * 



*The numbering reiers to the table at the end of the paper. 



