Replacing cell values

Hi,

My requirement is to replace the cell values only for a given range. And my range is only the cell values in a given single column.
Below is the code I am using.

Sheets("Sheet1").Select
Range("A3", Range("A3").End(xlDown)).Select
Cells.Replace What:="smalldatetime", Replacement:="date", LookAt:=xlPart, _

But the issue I am facing is that the cell values are getting replaced in the columns B and C as well for the matching word, though columns B and C are not in the range specified.

Can anyone please guide me where I am going wrong.

Thanks in advance for help.