This problem is now reduced by the careful collection of samples, rigorous crosschecking and the use of newer techniques that can date minute samples.Volcanic rocks – such as tuff and basalt – can be used in dating because they are formed at a particular moment in time, during an eruption.In other words, artifacts found in the upper layers of a site will have been deposited more recently than those found in the lower layers.Cross-dating of sites, comparing geologic strata at one site with another location and extrapolating the relative ages in that manner, is still an important dating strategy used today, primarily when sites are far too old for absolute dates to have much meaning.Often when geologists examine rock outcrops like the one illustrated above they are interested in not only the types of rocks present, but the order in which they formed.When they put events in chronological order like they use Relative Dating.
(Remember, we are only able to determine whether something is older or younger compared to something else.) See this link for a thorough review of how relative dating is done.
Relative-dating techniques are nearly always applicable but are not precise and require calibration.
Correlation techniques are locally useful and depend on recognition of an event whose age is known, such as a volcanic eruption or a paleomagnetic reversal.
The same thing can be done with geologic features in a rock outcrop.
To do this geologists use the Laws of Relative Dating.