No. 1.] GIBSON — GEOLOGY OF HURON COUNTY. 3T 



County, as far as can be ascertaiaecl by borings, forming the 

 foundation rock, so to speak, of the Corniferous limestone, and 

 where this is absent, immediately underlying the so-called Water- 

 lime beds. 



The Guelph formation — the uppermost layer of the Middle 

 Silurian series — is only observed by means of borings at a 

 depth of about 1,000 feet from the surface of the ground, and 

 underlying the most recent deposit of rock salt. Of the presence 

 of the Clinton and Medina formations underlying the rock-salt 

 and gypsiferous shales of the Salina group, we have but doubtful 

 evidence ; and it is only by means of specimens of rock brought 

 up by the sand-pump, during the operation of boring, that we 

 arrive at the probability of their existence within the average 

 depth of 1,150 feet from the surface. The more important 

 exposures of rock observed within the limits of this district are 

 given in the following list proceeding from north to south : — 



1. The escarpments in Howick. 



2. The outcrop on the falls of the Ashfield River. 



3. The outcrop between the Townships of Ashfield and Col- 

 borne. 



4. The outcrop on the Maitland, one-half mile from Goderich. 



5. The outcrop on the 1st lot of the 1st range of Colborne. 



6. The outcrop on the Maitland, IJ miles from Goderich. 



The Corniferous limestone which is the essential rock-com- 

 ponent of the above exposures, occupies in Ontario a superficial 

 area of about 6,500 square nailes. It is, comparatively, a pure 

 limestone, containing no traces of magnesia which to a great 

 extent enters into the composition of many of our calcareous 

 formations. Its beds are abundantly charged with organic 

 remains, some of which are little more than aggregates of chalce- 

 donic quartz with intermingled calcium carbonate. Numerous 

 beds of chert or hornstone are also especially characteristic of 

 these limestones, giving the name Corniferous to the formation. 



1. Throughout the Township of Carrick, and extending south 

 into Howick, occur numerous outcrops of limestone, forming 

 escarpments from twenty to thirty -feet in height. These consist 

 for the most part of blue and grey limestones of the Corniferous 

 formation. Their sharp outlines and acute indentations seem to 

 point to the existence of violent denuding agencies, probably 

 contemporaneous with the re-clevation of Western Ontario to- 

 wards the end of the Glacial Drift. 



