Henry Sicks — On the Northern Palceozoic Rocks. 251 



depth, do not refute the doctrine of Plutonic heat, or of a great sea 

 of deep-seated fluid, as he supposes ; nor do they really lead to the 

 inference that the internal temperature is the result of actions going 

 on in the outer crust. They ^Drove rather, for the depth examined, 

 4042 feet only, that the increased upper heat may be due entirely 

 to some local or superficial cause, and that the internal heat there 

 is at a sufficient depth not to balance the effects at this comparatively 

 superficial point. 



The chief conclusions to be derived from the foregoing remarks 

 are, that igneous eruptions in Palseozoic time were chiefly con- 

 fined to the regions which became first submerged, and the im- 

 mediate cause of these outbursts seems to have been the weakness of 

 the pre-Cambrian crust at those parts, in consequence of the great 

 depression that had taken place, and from being too thin there to 

 resist the pressure from within, and to bear the weight of the super- 

 incumbent mass of soft sediment ; that the seat of igneous action at 

 that time was at a very considerable depth, as sediments which were 

 depressed to a depth of from 9 to 10 miles do not indicate that they 

 had been subjected to the effect of any great amount of heat ; that 

 sediments which have been buried under 50,000 feet of strata, and 

 which consequently must have been subjected to the conditions of 

 heat and pressure existing at that depth, are found not to be sensibly 

 altered ; that in the same rocks the passage of a trap-dyke caused a 

 very considerable change in the mineral ingredients in its neigh- 

 bourhood ; and hence that metamorphism as a rule may be assumed 

 to be due to proximity to intrusive matter, or to heat derived from 

 the interior of the earth, and not to pressure. 



Climate and Succession of Life. — The influence which the various 

 changes which took place in the earth's crust during Paleozoic time 

 had on the succession and development of life must have been great, 

 and no idea can be formed of the probable order in which progress 

 took place unless these various influences are thoroughly considered. 

 In reviewing these causes, I may be allowed to return to a period 

 but slightly touched upon in this paper, and which, in showing us 

 the very earliest known indications of life, must yield evidence of 

 importance. In the Laurentian rocks which formed the pre-Cam- 

 brian continents, we have indications in the beds of limestone of 

 an abundance of marine life of a low type, and in the graphite and 

 iron-ore of vegetation. The graphite is supposed by most authorities 

 to have been derived from algse or marine plants ; but I think that it 

 must have been derived from land vegetation, as it alone seems to 

 have that power or persistency of fibre sufficient to allow such 

 changes to have been produced in any great amount out of its 

 structure. Moreover, if algge could form beds of this description, 

 surely they would be much more frequent in the succession after- 

 wards, as an abundance of marine vegetation must have prevailed 

 where marine animals such as were then common occurred. Again, 

 the soft cellular structure of the algse renders them liable to yeiy 

 rapid decay, and hence of solution. The presence at this period of 

 limestone; iron-ore, and graphite, naturally calls to mind the con- 



