STATE GEOLOGIST. 71 



The Hamilton Group seems to play a very important part in 

 the geology of the northern portion of the peninsula, but in the 

 southern part of the State it has not yet been satisfactorily 

 identified From Thunder Bay it passes under the bed of Lake 

 Huron, and reappears upon the Canada shore, between Ben- 

 son's Creek and Cape Ipperwash or Kettle Point. Prom here, 

 as nearly as can be ascertained from the 1 eports of the Can- 

 adian survey, it passes southward in a belt about ten miles 

 wide to the south-eastern part of the county of Lambton, where 

 it is met by another outcropping belt, extending east from the 

 shores of Lake St. Clair. The united belts fill a trough in the 

 Helderberg limestone, which extends east to the shore of Lake 

 Erie between Point aux Pirs and Long Point, whence it crosses 

 the lake, and reappears in Ohio. 



The branch which comes in from the direction of Lake St. 

 Clair, ought to be recognized in the southern part of our penin- 

 sula, but though we have here a great thickness of argillaceous 

 strata; they are supposed to belong rather to the group above 

 than to this one. It seems, at any late, pretty obvious that the 

 eminently fossiliferous limestones of Thunder and Little Tra- 

 verse Bays, do not reach Kie latitude of Detroit, a fact which 

 accords with the greni attenuation of the Helderberg lime- 

 stones, in the sam^ uirectien. 



In an economical point of view, the rocks of this group have 

 not been siiown to possess great interest. It would certainly 

 be "well, however, to test the hydraulic properties of some of 

 the argillaceous limestones of Thunder Bay. 



10. — Huron Group. 



At Sulphur Island, in Thunder Bay, not more than a mile 

 east south-east from Partridge Pt., is found a black bituminous 

 slate, which is believed to overlie the fossiliferous cliffs at the 

 latter place. No undisturbed strata are seen on the Island, 

 which consists of a mass of fragments rising a few feet above 

 the water. These slates or shales burn with considerable free- 

 dom, and it is stated that a combustion started from camp fires 

 has, in several instances, continued spontaneously for many 



