No. 5.] SPENCER — SURFACE GEOLOGY. 309 



One deposit now completed does not belong to this class. 

 Just west of the Catholic cemetery at Hamilton and bordering 

 on a branch of the Dundas marsh we find a bed of shell marl. 

 This is almost entirely made up of broken shells, and contains 

 also the following modern species in a state of preservation : — 

 Patida alteruata, Triodopsls trldeafata, Mesodon alholahri, 

 Succiiiea, ohliqna, as recognized by Mr. Whiteaves. This deposit 

 has a thickness of about 15 feet extending to that height above 

 the marsh. 



Some interesting facts with regard to the modern deposits in 

 our lake and the Dundas marsh have recently come to light. 

 The area of the Dundas marsh is rather more than two miles. It 

 is generally shallow and filled with reeds. In the eastern portion 

 there are some deeper places where the reeds do not grow, it is 

 being rapidly filled by the accumulations of the sediments from 

 the streams emptying into it. The deposits are now principally 

 made during the increased flow of water of the spring fresh- 

 ets. A constant source of trouble has for many years been 

 experienced by the silting up of the Desjardin canal, which 

 passes through the marsh. As late as I860 or 18G5 the western 

 end of the marsh was frequented for skating purposes; the same 

 portion is now turned into fertile meadows. For nearly a score 

 of years the proprietors have been trying to recover the land by 

 making dykes. One dyke after another has been encroaching on 

 the marsh until a considerable area is now drained. In making 

 one of these dykes a trench was sunk to a depth of several feet, 

 and at six and one-half feet from the surface Mr. James Cheo- 

 win came on a bed of saw-dust six inches in thickness. This 

 was in the year 1876. On making inquiry, I learned that the 

 first saw-mill in the region began operations about the year 1811. 

 Thus we see that from the time that the saw-dust was brought 

 down from Mr. Green's mill, in the Lindsay creek, a deposit of 

 mud six and one half feet thick accumulated in a period of about 

 sixty-five years, or that the rate of deposit is about a tenth of an 

 inch per annum. It is probable that at the present time the 

 accumulation is more rapid as the area of the deposit has been 

 considerably lessened. The parts of the marsh outside and adja- 

 cent to the dykes are now entirely above water in the later portion 

 of the summer. This setting up is continuing until the spring 

 freshets can no longer overflow the low land, when all the sedi- 

 ments are carried into deeper water. Seasons of high water in 



