No. 5.] SPENCER — SURFACE GEOLOGY. 311 



The greatest fluctuation in the 21 years was 3.1 feet, at 

 Toronto (omitting the four years '57, '61, '66, '69). From 

 these fluctuations of the lake it can be seen that the position of 

 the greatest deposition in the marsh will be somewhat changed 

 in different years, as much of it is very near the water level. 

 Durim>- a continuance of vears of low water the sediments would 

 be carried farther by the streams and consequently the higher 

 i>;rounds would not receive additions. 



Filling up the Western End of Burlington Biij. — Grindstone 

 creek empties into the western end of Burlington bay, and the 

 currents principally pass close to the eastern side of Burlington 

 Heights. As this stream brings down a large quantity of mud 

 and, although emptying first into a swamp of its own), a consid- 

 erable amount of sediment is carried into the bay and is deposited 

 in the quieter waters near Carrol's point, at which place there is 

 a long bar (submerged at high water) where these currents meet 

 the waves of the open bay. This portion of the bay is fast 

 becoming a swamp. 



XII. — LAKE MEDAD. 



About two miles northward of Waterdown, there is a small 

 pond — Lake Medad — half a mile long. In the western part of 

 Dundas valley there is a number of small ponds amongst the 

 hills of drift material, but these are only small expansions of the 

 various streams at heiirhts from 510 feet to 240 feet above the 

 level of Lake Ontario. On one side of Lake 3Iedad there is a 

 rugged shore of deeply weathered dolomites, extending more than 

 20 feet above its waters. The shore beneath is com])Osed of a beach 

 of pebbles. The opposite side of the lake is shallow, and is now 

 occupied by a marsh. This lakelet is not an expansion of any mo- 

 dern rivulet. A number of insignificant streams empty into it, but 

 not one of which could possibly have excavated the present basin. 

 This lakelet is not on the uppermost portion of the Niagara es- 

 carpment, but in a somewhat broadly rugged country. The basin 

 of Lake Medad is evidently a tilled up portion of a larger water 

 channel that became blocked by drift material, which it has been 

 unable to clean out for itself in modern times. The whole lake 

 could be drained by cutting through the drift deposits which 

 occupy one of its extremities. I was informed by one of the 

 inhabitants that he had discovered an underground outlet, so that 

 a portion of the waters discharge by a stream directly into Lake 



