148 



NOTES ON THE GEOLOGY OF TORONTO. 



[1853 



been divided in two lesser groups, called the Upper and the 

 Lower, or more recently into the Upper, Middle and Lower 

 Silurian. Their united thickness in Wales has been estimated 

 at about seven thousand feet. On this continent they attain 

 much greater thickness. They constitute with one known excep- 

 tion the most ancient of all fossiliferous groups of rocks. During 

 the period of the deposition of the Lower Silurian rocks the sea 

 would appear to have presented an aspect of tranquillit)', for we 

 generally find their strata to preserve great horizoutality, and to 

 exhibit many of the characteristics of quiet and undisturbed 

 progression. Some of the layers are beautifully ripple marked, 

 as you may see from this sjjecimen which was procured from the 

 cliff near the New Garrison. Many of the vegetables they entomb 

 seem to have been fossilized in the spot where they grew, and the 

 casts of shells in the soft horizontal shales, which are found abun- 

 dantly in this neighbourhood, exhibit minute markings when 

 examined mici'oscopically, in an admirable state of preservation. 



The Lower Silurian rocks consist of several formations of con- 

 siderable thickness which lie one over the other, and are the 

 representatives of extensive periods which elapsed during their 

 deposition. They are grouped because they contain in common 

 certain species of fossils, but their order of superposition exhibits 

 their relative ages, and their enormous thickness affords us a 

 vague idea of the immensity of the duration of the period of 

 which they are the record. In Western Canada the formations 

 which are analogous to those of the Lower Silurian group in 

 Britain, contain the subjoined subdivisions : — 



Primary Granite. 



1. Trenton Limestone. 



2. Utica Slate. 



2. Loraine Shales, (Caradoc Sandstone.) 



In the State of New York, and in some parts of Eastern 

 Canada, and the eastern part of Vv^esteru Canada, rocks older 

 than the Trenton Limestoae are to be found. It may be useful 

 to mention the names of these rocks in order to establish tlie 

 position of the Loraine Shales. The series would then be as 

 follows : — 



Primary Granite. 



1. Potsdam Sandstone. 



2. Calciferous Sandstone. 



3. Chazy Limestone. 



4. Birdseye " 



5. Black River " 



6. Trenton " 

 V. Utica Slates. 



8. Loraine Shales or Hudson River group. 



From the foregoing table we are to understand that the Pots- 

 dam Sandstone is the earliest, and consequently the lowest fossil- 

 iferous strata found in this country, — or as Mr. Hall states,* " as 

 having been produced at the dawning of the vital piinciple upon 

 our planet ; nothing which bears the semblance of having been 

 organic is yet known in strata of anterior origin." 



After the deposition of the Potsdam sandstone the Calciferous 

 sandstone occurred, then the Chazy, Birds-eye, Black River and 

 Trenton limestones were slowly accumulated one above the other, 

 each entombing an infinite multitude of the denizens of the seas 

 in wliieli they were deposited. After these came the Utica Slates, 

 and then the 1,000 feet thick Loraine Shales were slow!)-, and 

 probably peacefully piled up over a vast extent of the earth's 

 surface. 



The Hudson Ri\^cr group or Loraine Shales is the rock to 

 which we must I'cfer the strata which are exhibited at the Garri- 

 son C(jmmon. Mi'. Murray, tlie Assistant Provincial Geologist, 

 observes in the admirablo Geological Repoits, that the Loraine 



* PoliFontology of New Vork, 



Shales " compose the substrata of the whole country on the shore 

 of Lake Ontario, between the River Rouge, in the Townshipof 

 Pickering, on the East, and the River Credit, in Toronto Town- 

 ship, on the West, and sections of them may be seen in almost 

 all the streams that intervene between the one point and the 

 other." 



" The estimate I (Mr. MuiTay) have made of their thickness 

 brings it to 1,110 feet. How near this may approach the truth 

 is difficult to say, but the result of such e\'ideuce as I have had 

 it in my power to collect being still in f;ivour of supposing the 

 dip to be at about the rate of thirty feet to the mile, it is proba- 

 ble that the figures giNen constitute a tolerable approximation." 



That the Loraine shales belong to the Lower Silurian group of 

 Sir Roderick Murchison we have the subjoined authority of Mr. 

 Hall. 



" Commencing at the lowest rock known to contain fossils, we 

 find the most important change in the typical forms to occur at 

 the termination of the Hudson River group, (Loraine Shales) 

 which is marked by a coai-se sandstone or conglomerate, beyond 

 which scarcely a single species has prolonged its existence. This 

 point must be considered as representing that Horizon which in 

 Great Britain is the termination of the Lower Silurian deposits. 

 We never find, however, in the succeeding groups, a mingling of 

 the fossils of the Lower and Higher rocks, which is regarded as 

 takiua; place in England and Wales, where the strata aie much 

 disturbed. (Hall, 1 alffiontology of New York.) 



The Lower Silurian period and its relative distance in time 

 from the present epoch, may be represented by the following 

 table of the thickness of deposits which have accumulated since 

 its termination; that is, since the time of the layei-s of sandstone 

 and shale which we see at the Garrison Common beach : — 



{Containing a small 

 number of fossils 

 identical with exist- 

 ing species. 



Containing fossils 

 belono-ino- altosreth- 



Rocks of the Middle or Mesozoic 

 period. 



feet 

 5100 



Rocks of the Ancient or Paleozoic 

 period. 



er to extinct species. 



Containing fossils 



belonging not only 



feet J to extinct species 



21,000 I but also often to 



extinct genera and 



families. 



Above the Loraine Shales we find an aggregate of fossiliferous 

 strata having a thickness exceeding 26,000 feet, or five miles, 

 not represented at Toronto, but which are ne^■ertI^eless illustrative 

 of that immense period which has endured since the formation 

 which underlies the Drift upon which Toronto is built, was slowly 

 and perhaps tranquilly accumulated. 



The relation of the Drift and Loraine Shales may be familiarly 

 shown by dividing a line into thirty equal parts, and numbering 

 them 1, 2, 3, 4, 5, &c., the position of the drift would bo ap- 

 proximately represented by the 1st division, the Loraine Shales by 

 the 26th division, and the true Coal Measures by the 15th 

 division. From the 27th division to the thirtieth, we should 

 have the rocks which were formed before the Loraine Shales and 

 the probable dawn of life upon the surface of the Globe. It is an 

 important question in this country to ascertain the relation which 

 exists in time between the true coal measures and the Loraine 

 Shales; this may be roughly and generally represented by a 

 series of formations ; having a thickness of 12000 foot, which we 

 may suppose to be placed between the uppermost layerof the 

 Shales and the lowest stratum of true coal. And furthoi', if we 

 assume that the vast Devonian group has no representative in 



