14 PERMO-CARBONIFEROUS FOSSIL CLIFFS. 



associates. Orlo;lnally, in my larger work, on " The 

 Geolq<2:y of Tasmania," for the sake of convenience in 

 description, I provisionally divided the varions members 

 of the Permo-Carboniferous rocks at this place into 

 three great divisions or zones, part i haracterised by 

 differences in the prevailing forms of fossil life, and 

 partly by a considerable difference in the character 

 and composition of the successive beds or groups of 

 strata. 



(1.) Erratic Zone. — The lowest beds visible above 

 sea-level have been termed by me TJie Erratic Zone. 

 Composed of more or less impure limestones, frequently 

 studded with great erratic boulders of quartzites, slates, 

 schists, and granites or conglomerates of these older 

 rocks, cemented together by limestone. Some of these 

 huge, angular, erratic granite blocks weigh over a ton. 



There is abundant evidence now to show that these 

 huge erratics must have been borne thither by meeting 

 ice-sheets. Similar evidence of glacial action during 

 the age in which these rocks were formed, occur in 

 England ; Talchir and Salt Kange, India ; Dwyka 

 Conglomerates, South Africa : Bacchus Marsh Con- 

 glomerates, Victoria ; New South Wales ; and in many 

 parts of Tasmania, in rocks of the same horizon. Fuller 

 details of glacial evidence are given in my observations 

 on " The Glacier Epoch of Australia," read before the 

 Members of this Society, in the year 1893. (See Papers 

 and Proceedings of Royal Society of Tasmania, June. 

 1893.) 



(2.) Pachydomns Zone. — Immediately above the Er- 

 ratic Zone occurs a series of alternating beds of cal- 

 careous shale and solid limestones, characterised con- 

 spicuously by the prevalence of the large globose 

 bivalves of the genus Pachydomus. This series, or Zone, 

 is about eighty feet in thickness, and w^as termed by me 

 originally the Pachydomus Zone. It must not be inferred, 

 however, that this genus is solely confined to this division, 

 or that this genus alone is to be found within the limits 

 of the zone so named. All that is intended here, by the 

 classified name, is, that in this group of beds, the genus 

 Pachydomus dominates supremely over all other forms of 

 life, and a forty-feet bed is almost wholly composed of 

 their fossils. The following is a fairly typical list of 



